diff --git a/Source/Core/DiscIO/CMakeLists.txt b/Source/Core/DiscIO/CMakeLists.txt
index 1729f0d959..9f0e7b6cde 100644
--- a/Source/Core/DiscIO/CMakeLists.txt
+++ b/Source/Core/DiscIO/CMakeLists.txt
@@ -28,6 +28,8 @@ add_library(discio
   MultithreadedCompressor.h
   NANDImporter.cpp
   NANDImporter.h
+  RiivolutionParser.cpp
+  RiivolutionParser.h
   ScrubbedBlob.cpp
   ScrubbedBlob.h
   TGCBlob.cpp
diff --git a/Source/Core/DiscIO/RiivolutionParser.cpp b/Source/Core/DiscIO/RiivolutionParser.cpp
new file mode 100644
index 0000000000..3162c40d43
--- /dev/null
+++ b/Source/Core/DiscIO/RiivolutionParser.cpp
@@ -0,0 +1,336 @@
+// Copyright 2021 Dolphin Emulator Project
+// SPDX-License-Identifier: GPL-2.0-or-later
+
+#include "DiscIO/RiivolutionParser.h"
+
+#include <algorithm>
+#include <string>
+#include <string_view>
+#include <vector>
+
+#include <pugixml.hpp>
+
+#include "Common/FileUtil.h"
+#include "Common/IOFile.h"
+#include "Common/StringUtil.h"
+
+namespace DiscIO::Riivolution
+{
+std::optional<Disc> ParseFile(const std::string& filename)
+{
+  ::File::IOFile f(filename, "rb");
+  if (!f)
+    return std::nullopt;
+
+  std::vector<char> data;
+  data.resize(f.GetSize());
+  if (!f.ReadBytes(data.data(), data.size()))
+    return std::nullopt;
+
+  return ParseString(std::string_view(data.data(), data.size()), filename);
+}
+
+static std::map<std::string, std::string> ReadParams(const pugi::xml_node& node,
+                                                     std::map<std::string, std::string> params = {})
+{
+  for (const auto& param_node : node.children("param"))
+  {
+    const std::string param_name = param_node.attribute("name").as_string();
+    const std::string param_value = param_node.attribute("value").as_string();
+    params[param_name] = param_value;
+  }
+  return params;
+}
+
+static std::vector<u8> ReadHexString(std::string_view sv)
+{
+  if ((sv.size() % 2) == 1)
+    return {};
+  if (StringBeginsWith(sv, "0x") || StringBeginsWith(sv, "0X"))
+    sv = sv.substr(2);
+
+  std::vector<u8> result;
+  result.reserve(sv.size() / 2);
+  while (!sv.empty())
+  {
+    u8 tmp;
+    if (!TryParse(std::string(sv.substr(0, 2)), &tmp, 16))
+      return {};
+    result.push_back(tmp);
+    sv = sv.substr(2);
+  }
+  return result;
+};
+
+std::optional<Disc> ParseString(std::string_view xml, std::string xml_path)
+{
+  pugi::xml_document doc;
+  const auto parse_result = doc.load_buffer(xml.data(), xml.size());
+  if (!parse_result)
+    return std::nullopt;
+
+  const auto wiidisc = doc.child("wiidisc");
+  if (!wiidisc)
+    return std::nullopt;
+
+  Disc disc;
+  disc.m_xml_path = std::move(xml_path);
+  disc.m_version = wiidisc.attribute("version").as_int(-1);
+  if (disc.m_version != 1)
+    return std::nullopt;
+  const std::string default_root = wiidisc.attribute("root").as_string();
+
+  const auto id = wiidisc.child("id");
+  if (id)
+  {
+    for (const auto& attribute : id.attributes())
+    {
+      const std::string_view attribute_name(attribute.name());
+      if (attribute_name == "game")
+        disc.m_game_filter.m_game = attribute.as_string();
+      else if (attribute_name == "developer")
+        disc.m_game_filter.m_developer = attribute.as_string();
+      else if (attribute_name == "disc")
+        disc.m_game_filter.m_disc = attribute.as_int(-1);
+      else if (attribute_name == "version")
+        disc.m_game_filter.m_version = attribute.as_int(-1);
+    }
+
+    auto xml_regions = id.children("region");
+    if (xml_regions.begin() != xml_regions.end())
+    {
+      std::vector<std::string> regions;
+      for (const auto& region : xml_regions)
+        regions.push_back(region.attribute("type").as_string());
+      disc.m_game_filter.m_regions = std::move(regions);
+    }
+  }
+
+  const auto options = wiidisc.child("options");
+  if (options)
+  {
+    for (const auto& section_node : options.children("section"))
+    {
+      Section& section = disc.m_sections.emplace_back();
+      section.m_name = section_node.attribute("name").as_string();
+      for (const auto& option_node : section_node.children("option"))
+      {
+        Option& option = section.m_options.emplace_back();
+        option.m_id = option_node.attribute("id").as_string();
+        option.m_name = option_node.attribute("name").as_string();
+        option.m_selected_choice = option_node.attribute("default").as_uint(0);
+        auto option_params = ReadParams(option_node);
+        for (const auto& choice_node : option_node.children("choice"))
+        {
+          Choice& choice = option.m_choices.emplace_back();
+          choice.m_name = choice_node.attribute("name").as_string();
+          auto choice_params = ReadParams(choice_node, option_params);
+          for (const auto& patchref_node : choice_node.children("patch"))
+          {
+            PatchReference& patchref = choice.m_patch_references.emplace_back();
+            patchref.m_id = patchref_node.attribute("id").as_string();
+            patchref.m_params = ReadParams(patchref_node, choice_params);
+          }
+        }
+      }
+    }
+    for (const auto& macro_node : options.children("macros"))
+    {
+      const std::string macro_id = macro_node.attribute("id").as_string();
+      for (auto& section : disc.m_sections)
+      {
+        auto option_to_clone = std::find_if(section.m_options.begin(), section.m_options.end(),
+                                            [&](const Option& o) { return o.m_id == macro_id; });
+        if (option_to_clone == section.m_options.end())
+          continue;
+
+        Option cloned_option = *option_to_clone;
+        cloned_option.m_name = macro_node.attribute("name").as_string();
+        for (auto& choice : cloned_option.m_choices)
+          for (auto& patch_ref : choice.m_patch_references)
+            patch_ref.m_params = ReadParams(macro_node, patch_ref.m_params);
+      }
+    }
+  }
+
+  const auto patches = wiidisc.children("patch");
+  for (const auto& patch_node : patches)
+  {
+    Patch& patch = disc.m_patches.emplace_back();
+    patch.m_id = patch_node.attribute("id").as_string();
+    patch.m_root = patch_node.attribute("root").as_string();
+    if (patch.m_root.empty())
+      patch.m_root = default_root;
+
+    for (const auto& patch_subnode : patch_node.children())
+    {
+      const std::string_view patch_name(patch_subnode.name());
+      if (patch_name == "file")
+      {
+        auto& file = patch.m_file_patches.emplace_back();
+        file.m_disc = patch_subnode.attribute("disc").as_string();
+        file.m_external = patch_subnode.attribute("external").as_string();
+        file.m_resize = patch_subnode.attribute("resize").as_bool(true);
+        file.m_create = patch_subnode.attribute("create").as_bool(false);
+        file.m_offset = patch_subnode.attribute("offset").as_uint(0);
+        file.m_fileoffset = patch_subnode.attribute("fileoffset").as_uint(0);
+        file.m_length = patch_subnode.attribute("length").as_uint(0);
+      }
+      else if (patch_name == "folder")
+      {
+        auto& folder = patch.m_folder_patches.emplace_back();
+        folder.m_disc = patch_subnode.attribute("disc").as_string();
+        folder.m_external = patch_subnode.attribute("external").as_string();
+        folder.m_resize = patch_subnode.attribute("resize").as_bool(true);
+        folder.m_create = patch_subnode.attribute("create").as_bool(false);
+        folder.m_recursive = patch_subnode.attribute("recursive").as_bool(true);
+        folder.m_length = patch_subnode.attribute("length").as_uint(0);
+      }
+      else if (patch_name == "savegame")
+      {
+        auto& savegame = patch.m_savegame_patches.emplace_back();
+        savegame.m_external = patch_subnode.attribute("external").as_string();
+        savegame.m_clone = patch_subnode.attribute("clone").as_bool(true);
+      }
+      else if (patch_name == "memory")
+      {
+        auto& memory = patch.m_memory_patches.emplace_back();
+        memory.m_offset = patch_subnode.attribute("offset").as_uint(0);
+        memory.m_value = ReadHexString(patch_subnode.attribute("value").as_string());
+        memory.m_valuefile = patch_subnode.attribute("valuefile").as_string();
+        memory.m_original = ReadHexString(patch_subnode.attribute("original").as_string());
+        memory.m_ocarina = patch_subnode.attribute("ocarina").as_bool(false);
+        memory.m_search = patch_subnode.attribute("search").as_bool(false);
+        memory.m_align = patch_subnode.attribute("align").as_uint(1);
+      }
+    }
+  }
+
+  return disc;
+}
+
+static bool CheckRegion(const std::vector<std::string>& xml_regions, std::string_view game_region)
+{
+  if (xml_regions.begin() == xml_regions.end())
+    return true;
+
+  for (const auto& region : xml_regions)
+  {
+    if (region == game_region)
+      return true;
+  }
+
+  return false;
+}
+
+bool Disc::IsValidForGame(const std::string& game_id, std::optional<u16> revision,
+                          std::optional<u8> disc_number) const
+{
+  if (game_id.size() != 6)
+    return false;
+
+  const std::string_view game_id_full = std::string_view(game_id);
+  const std::string_view game_region = game_id_full.substr(3, 1);
+  const std::string_view game_developer = game_id_full.substr(4, 2);
+  const int disc_number_int = std::optional<int>(disc_number).value_or(-1);
+  const int revision_int = std::optional<int>(revision).value_or(-1);
+
+  if (m_game_filter.m_game && !StringBeginsWith(game_id_full, *m_game_filter.m_game))
+    return false;
+  if (m_game_filter.m_developer && game_developer != *m_game_filter.m_developer)
+    return false;
+  if (m_game_filter.m_disc && disc_number_int != *m_game_filter.m_disc)
+    return false;
+  if (m_game_filter.m_version && revision_int != *m_game_filter.m_version)
+    return false;
+  if (m_game_filter.m_regions && !CheckRegion(*m_game_filter.m_regions, game_region))
+    return false;
+
+  return true;
+}
+
+std::vector<Patch> Disc::GeneratePatches(const std::string& game_id) const
+{
+  const std::string_view game_id_full = std::string_view(game_id);
+  const std::string_view game_id_no_region = game_id_full.substr(0, 3);
+  const std::string_view game_region = game_id_full.substr(3, 1);
+  const std::string_view game_developer = game_id_full.substr(4, 2);
+
+  const auto replace_variables =
+      [&](std::string_view sv,
+          const std::vector<std::pair<std::string, std::string_view>>& replacements) {
+        std::string result;
+        result.reserve(sv.size());
+        while (!sv.empty())
+        {
+          bool replaced = false;
+          for (const auto& r : replacements)
+          {
+            if (StringBeginsWith(sv, r.first))
+            {
+              for (char c : r.second)
+                result.push_back(c);
+              sv = sv.substr(r.first.size());
+              replaced = true;
+              break;
+            }
+          }
+          if (replaced)
+            continue;
+          result.push_back(sv[0]);
+          sv = sv.substr(1);
+        }
+        return result;
+      };
+
+  // Take only selected patches, replace placeholders in all strings, and return them.
+  std::vector<Patch> active_patches;
+  for (const auto& section : m_sections)
+  {
+    for (const auto& option : section.m_options)
+    {
+      const u32 selected = option.m_selected_choice;
+      if (selected == 0 || selected > option.m_choices.size())
+        continue;
+      const Choice& choice = option.m_choices[selected - 1];
+      for (const auto& patch_ref : choice.m_patch_references)
+      {
+        const auto patch = std::find_if(m_patches.begin(), m_patches.end(),
+                                        [&](const Patch& p) { return patch_ref.m_id == p.m_id; });
+        if (patch == m_patches.end())
+          continue;
+
+        std::vector<std::pair<std::string, std::string_view>> replacements;
+        replacements.emplace_back(std::pair{"{$__gameid}", game_id_no_region});
+        replacements.emplace_back(std::pair{"{$__region}", game_region});
+        replacements.emplace_back(std::pair{"{$__maker}", game_developer});
+        for (const auto& param : patch_ref.m_params)
+          replacements.emplace_back(std::pair{"{$" + param.first + "}", param.second});
+
+        Patch& new_patch = active_patches.emplace_back(*patch);
+        new_patch.m_root = replace_variables(new_patch.m_root, replacements);
+        for (auto& file : new_patch.m_file_patches)
+        {
+          file.m_disc = replace_variables(file.m_disc, replacements);
+          file.m_external = replace_variables(file.m_external, replacements);
+        }
+        for (auto& folder : new_patch.m_folder_patches)
+        {
+          folder.m_disc = replace_variables(folder.m_disc, replacements);
+          folder.m_external = replace_variables(folder.m_external, replacements);
+        }
+        for (auto& savegame : new_patch.m_savegame_patches)
+        {
+          savegame.m_external = replace_variables(savegame.m_external, replacements);
+        }
+        for (auto& memory : new_patch.m_memory_patches)
+        {
+          memory.m_valuefile = replace_variables(memory.m_valuefile, replacements);
+        }
+      }
+    }
+  }
+
+  return active_patches;
+}
+}  // namespace DiscIO::Riivolution
diff --git a/Source/Core/DiscIO/RiivolutionParser.h b/Source/Core/DiscIO/RiivolutionParser.h
new file mode 100644
index 0000000000..61b81be569
--- /dev/null
+++ b/Source/Core/DiscIO/RiivolutionParser.h
@@ -0,0 +1,193 @@
+// Copyright 2021 Dolphin Emulator Project
+// SPDX-License-Identifier: GPL-2.0-or-later
+
+#pragma once
+
+#include <map>
+#include <optional>
+#include <string>
+#include <string_view>
+#include <vector>
+
+#include "Common/CommonTypes.h"
+
+namespace DiscIO::Riivolution
+{
+// Data to determine the game patches are valid for.
+struct GameFilter
+{
+  std::optional<std::string> m_game;
+  std::optional<std::string> m_developer;
+  std::optional<int> m_disc;
+  std::optional<int> m_version;
+  std::optional<std::vector<std::string>> m_regions;
+};
+
+// Which patches will get activated by selecting a Choice in the Riivolution GUI.
+struct PatchReference
+{
+  std::string m_id;
+  std::map<std::string, std::string> m_params;
+};
+
+// A single choice within an Option in the Riivolution GUI.
+struct Choice
+{
+  std::string m_name;
+  std::vector<PatchReference> m_patch_references;
+};
+
+// A single option presented to the user in the Riivolution GUI.
+struct Option
+{
+  std::string m_name;
+  std::string m_id;
+  std::vector<Choice> m_choices;
+
+  // The currently selected patch choice in the m_choices vector.
+  // Note that this index is 1-based; 0 means no choice is selected and this Option is disabled.
+  u32 m_selected_choice;
+};
+
+// A single page of options presented to the user in the Riivolution GUI.
+struct Section
+{
+  std::string m_name;
+  std::vector<Option> m_options;
+};
+
+// Replaces, adds, or modifies a file on disc.
+struct File
+{
+  // Path of the file on disc to modify.
+  std::string m_disc;
+
+  // Path of the file on SD card to use for modification.
+  std::string m_external;
+
+  // If true, the file on the disc is truncated if the external file end is before the disc file
+  // end. If false, the bytes after the external file end stay as they were.
+  bool m_resize = true;
+
+  // If true, a new file is created if it does not already exist at the disc path. Otherwise this
+  // modification is ignored if the file does not exist on disc.
+  bool m_create = false;
+
+  // Offset of where to start replacing bytes in the on-disc file.
+  u32 m_offset = 0;
+
+  // Offset of where to start reading bytes in the external file.
+  u32 m_fileoffset = 0;
+
+  // Amount of bytes to copy from the external file to the disc file.
+  // If left zero, the entire file (starting at fileoffset) is used.
+  u32 m_length = 0;
+};
+
+// Adds or modifies a folder on disc.
+struct Folder
+{
+  // Path of the folder on disc to modify.
+  // Can be left empty to replace files matching the filename without specifying the folder.
+  std::string m_disc;
+
+  // Path of the folder on SD card to use for modification.
+  std::string m_external;
+
+  // Like File::m_resize but for each file in the folder.
+  bool m_resize = true;
+
+  // Like File::m_create but for each file in the folder.
+  bool m_create = false;
+
+  // Whether to also traverse subdirectories. (TODO: of the disc folder? external folder? both?)
+  bool m_recursive = true;
+
+  // Like File::m_length but for each file in the folder.
+  u32 m_length = 0;
+};
+
+// Redirects the save file from the Wii NAND to a folder on SD card.
+struct Savegame
+{
+  // The folder on SD card to use for the save files. Is created if it does not exist.
+  std::string m_external;
+
+  // If this is set to true and the external folder is empty or does not exist, the existing save on
+  // NAND is copied to the new folder on game boot.
+  bool m_clone = true;
+};
+
+// Modifies the game RAM right before jumping into the game executable.
+struct Memory
+{
+  // Memory address where this modification takes place.
+  u32 m_offset = 0;
+
+  // Bytes to write to that address.
+  std::vector<u8> m_value;
+
+  // Like m_value, but read the bytes from a file instead.
+  std::string m_valuefile;
+
+  // If set, the memory at that address will be checked before the value is written, and the
+  // replacement value only written if the bytes there match this.
+  std::vector<u8> m_original;
+
+  // If true, this memory patch is an ocarina-style patch.
+  // TODO: I'm unsure what this means exactly, need to check some examples...
+  bool m_ocarina = false;
+
+  // If true, the offset is not known, and instead we should search for the m_original bytes in
+  // memory and replace them where found. Only searches in MEM1, and only replaces the first match.
+  bool m_search = false;
+
+  // For m_search. The byte stride between search points.
+  u32 m_align = 1;
+};
+
+struct Patch
+{
+  // Internal name of this patch.
+  std::string m_id;
+
+  // Defines a SD card path that all other paths are relative to.
+  // We need to manually set this somehow because we have no SD root, and should ignore the path
+  // from the XML.
+  std::string m_root;
+
+  std::vector<File> m_file_patches;
+  std::vector<Folder> m_folder_patches;
+  std::vector<Savegame> m_savegame_patches;
+  std::vector<Memory> m_memory_patches;
+};
+
+struct Disc
+{
+  // Riivolution version. Only '1' exists at time of writing.
+  int m_version;
+
+  // Info about which game and revision these patches are for.
+  GameFilter m_game_filter;
+
+  // The options shown to the user in the UI.
+  std::vector<Section> m_sections;
+
+  // The actual patch instructions.
+  std::vector<Patch> m_patches;
+
+  // The path to the parsed XML file.
+  std::string m_xml_path;
+
+  // Checks whether these patches are valid for the given game.
+  bool IsValidForGame(const std::string& game_id, std::optional<u16> revision,
+                      std::optional<u8> disc_number) const;
+
+  // Transforms an abstract XML-parsed patch set into a concrete one, with only the selected
+  // patches applied and all placeholders replaced.
+  std::vector<Patch> GeneratePatches(const std::string& game_id) const;
+};
+
+std::optional<Disc> ParseFile(const std::string& filename);
+std::optional<Disc> ParseString(std::string_view xml, std::string xml_path);
+}  // namespace DiscIO::Riivolution
diff --git a/Source/Core/DolphinLib.props b/Source/Core/DolphinLib.props
index 59c862f1dd..b795b8533c 100644
--- a/Source/Core/DolphinLib.props
+++ b/Source/Core/DolphinLib.props
@@ -433,6 +433,7 @@
     <ClInclude Include="DiscIO\LaggedFibonacciGenerator.h" />
     <ClInclude Include="DiscIO\MultithreadedCompressor.h" />
     <ClInclude Include="DiscIO\NANDImporter.h" />
+    <ClInclude Include="DiscIO\RiivolutionParser.h" />
     <ClInclude Include="DiscIO\ScrubbedBlob.h" />
     <ClInclude Include="DiscIO\TGCBlob.h" />
     <ClInclude Include="DiscIO\Volume.h" />
@@ -1019,6 +1020,7 @@
     <ClCompile Include="DiscIO\FileSystemGCWii.cpp" />
     <ClCompile Include="DiscIO\LaggedFibonacciGenerator.cpp" />
     <ClCompile Include="DiscIO\NANDImporter.cpp" />
+    <ClCompile Include="DiscIO\RiivolutionParser.cpp" />
     <ClCompile Include="DiscIO\ScrubbedBlob.cpp" />
     <ClCompile Include="DiscIO\TGCBlob.cpp" />
     <ClCompile Include="DiscIO\Volume.cpp" />