diff --git a/CMakeLists.txt b/CMakeLists.txt
index 06201c84..ca81fad1 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -182,6 +182,7 @@ set (LOOT_API_SRC "${CMAKE_BINARY_DIR}/generated/loot_version.cpp"
                   "${CMAKE_SOURCE_DIR}/src/api/metadata_list.cpp"
                   "${CMAKE_SOURCE_DIR}/src/api/masterlist.cpp"
                   "${CMAKE_SOURCE_DIR}/src/api/plugin.cpp"
+                  "${CMAKE_SOURCE_DIR}/src/api/sorting/group_sort.cpp"
                   "${CMAKE_SOURCE_DIR}/src/api/sorting/plugin_sorter.cpp"
                   "${CMAKE_SOURCE_DIR}/src/api/sorting/plugin_sorting_data.cpp"
                   "${CMAKE_SOURCE_DIR}/src/api/helpers/crc.cpp"
@@ -233,6 +234,7 @@ set (LOOT_API_HEADERS "${CMAKE_SOURCE_DIR}/include/loot/api.h"
                       "${CMAKE_SOURCE_DIR}/src/api/metadata_list.h"
                       "${CMAKE_SOURCE_DIR}/src/api/masterlist.h"
                       "${CMAKE_SOURCE_DIR}/src/api/plugin.h"
+                      "${CMAKE_SOURCE_DIR}/src/api/sorting/group_sort.h"
                       "${CMAKE_SOURCE_DIR}/src/api/sorting/plugin_sorter.h"
                       "${CMAKE_SOURCE_DIR}/src/api/sorting/plugin_sorting_data.h"
                       "${CMAKE_SOURCE_DIR}/src/api/helpers/git_helper.h"
@@ -263,6 +265,7 @@ set (LOOT_TESTS_HEADERS "${CMAKE_SOURCE_DIR}/src/tests/api/internals/game/game_t
                         "${CMAKE_SOURCE_DIR}/src/tests/api/internals/metadata/priority_test.h"
                         "${CMAKE_SOURCE_DIR}/src/tests/api/internals/metadata/tag_test.h"
                         "${CMAKE_SOURCE_DIR}/src/tests/api/internals/plugin_test.h"
+                        "${CMAKE_SOURCE_DIR}/src/tests/api/internals/sorting/group_sort_test.h"
                         "${CMAKE_SOURCE_DIR}/src/tests/api/internals/sorting/plugin_sorter_test.h"
                         "${CMAKE_SOURCE_DIR}/src/tests/api/internals/masterlist_test.h"
                         "${CMAKE_SOURCE_DIR}/src/tests/api/internals/metadata_list_test.h"
diff --git a/src/api/sorting/group_sort.cpp b/src/api/sorting/group_sort.cpp
new file mode 100644
index 00000000..bb674249
--- /dev/null
+++ b/src/api/sorting/group_sort.cpp
@@ -0,0 +1,135 @@
+/*  LOOT
+
+    A load order optimisation tool for Oblivion, Skyrim, Fallout 3 and
+    Fallout: New Vegas.
+
+    Copyright (C) 2018    WrinklyNinja
+
+    This file is part of LOOT.
+
+    LOOT is free software: you can redistribute
+    it and/or modify it under the terms of the GNU General Public License
+    as published by the Free Software Foundation, either version 3 of
+    the License, or (at your option) any later version.
+
+    LOOT is distributed in the hope that it will
+    be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of
+    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+    GNU General Public License for more details.
+
+    You should have received a copy of the GNU General Public License
+    along with LOOT.  If not, see
+    <https://www.gnu.org/licenses/>.
+    */
+
+#include "group_sort.h"
+
+#include <boost/graph/adjacency_list.hpp>
+#include <boost/graph/graph_traits.hpp>
+#include <boost/graph/depth_first_search.hpp>
+
+#include "loot/exception/cyclic_interaction_error.h"
+
+namespace loot {
+typedef boost::adjacency_list<boost::vecS,
+                              boost::vecS,
+                              boost::directedS,
+                              std::string> GroupGraph;
+typedef boost::graph_traits<GroupGraph>::vertex_descriptor vertex_t;
+typedef boost::graph_traits<GroupGraph>::edge_descriptor edge_t;
+
+class GroupCycleDetector : public boost::dfs_visitor<> {
+public:
+  void tree_edge(edge_t edge, const GroupGraph& graph) {
+    auto source = boost::source(edge, graph);
+    auto name = graph[source];
+
+    // Check if the plugin already exists in the recorded trail.
+    auto it = find(begin(trail), end(trail), name);
+
+    if (it != end(trail)) {
+      // Erase everything from this position onwards, as it doesn't
+      // contribute to a forward-cycle.
+      trail.erase(it, end(trail));
+    }
+
+    trail.push_back(name);
+  }
+
+  void back_edge(edge_t edge, const GroupGraph& graph) {
+    auto source = boost::source(edge, graph);
+    auto target = boost::target(edge, graph);
+
+    trail.push_back(graph[source]);
+    std::string backCycle;
+    auto it = find(begin(trail), end(trail), graph[target]);
+    for (it; it != end(trail); ++it) {
+      backCycle += *it + ", ";
+    }
+    backCycle.erase(backCycle.length() - 2);
+
+    throw CyclicInteractionError(
+        graph[source], graph[target], backCycle);
+  }
+
+private:
+  std::vector<std::string> trail;
+};
+
+class AfterGroupsVisitor : public boost::dfs_visitor<> {
+public:
+  AfterGroupsVisitor(std::unordered_set<std::string>& visitedGroups) : visitedGroups_(visitedGroups) {}
+  void tree_edge(edge_t edge, const GroupGraph& graph) {
+    auto target = boost::target(edge, graph);
+    visitedGroups_.insert(graph[target]);
+  }
+
+  std::unordered_set<std::string> get_visited_groups() const {
+    return visitedGroups_;
+  }
+private:
+  std::unordered_set<std::string>& visitedGroups_;
+};
+
+std::unordered_map<std::string, std::unordered_set<std::string>> GetTransitiveAfterGroups(const std::unordered_set<Group> groups) {
+  GroupGraph graph;
+
+  std::unordered_map<std::string, vertex_t> groupVertices;
+  for (const auto& group : groups) {
+      auto vertex = boost::add_vertex(group.GetName(), graph);
+      groupVertices.emplace(group.GetName(), vertex);
+  }
+
+  for (const auto& group : groups) {
+    for (const auto& otherGroupName : group.GetAfterGroups()) {
+      auto otherVertex = groupVertices.find(otherGroupName);
+      if (otherVertex == groupVertices.end()) {
+        throw std::invalid_argument("The group \"" + otherGroupName + "\" does not exist");
+      }
+
+      auto vertex = groupVertices[group.GetName()];
+      boost::add_edge(vertex, otherVertex->second, graph);
+    }
+  }
+
+  // Check for cycles.
+  boost::depth_first_search(graph, visitor(GroupCycleDetector()));
+
+  std::unordered_map<std::string, std::unordered_set<std::string>> transitiveAfterGroups;
+  for (const vertex_t& vertex : boost::make_iterator_range(boost::vertices(graph))) {
+    std::unordered_set<std::string> visitedGroups;
+    AfterGroupsVisitor afterGroupsVisitor(visitedGroups);
+
+    // Create a color map.
+    std::vector<boost::default_color_type> colorVec(boost::num_vertices(graph));
+    auto colorMap = boost::make_iterator_property_map(colorVec.begin(),
+      boost::get(boost::vertex_index, graph),
+      colorVec[0]);
+
+    boost::depth_first_visit(graph, vertex, afterGroupsVisitor, colorMap);
+    transitiveAfterGroups[graph[vertex]] = visitedGroups;
+  }
+
+  return transitiveAfterGroups;
+}
+}
diff --git a/src/api/sorting/group_sort.h b/src/api/sorting/group_sort.h
new file mode 100644
index 00000000..6ba46bb2
--- /dev/null
+++ b/src/api/sorting/group_sort.h
@@ -0,0 +1,38 @@
+/*  LOOT
+
+    A load order optimisation tool for Oblivion, Skyrim, Fallout 3 and
+    Fallout: New Vegas.
+
+    Copyright (C) 2018    WrinklyNinja
+
+    This file is part of LOOT.
+
+    LOOT is free software: you can redistribute
+    it and/or modify it under the terms of the GNU General Public License
+    as published by the Free Software Foundation, either version 3 of
+    the License, or (at your option) any later version.
+
+    LOOT is distributed in the hope that it will
+    be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of
+    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+    GNU General Public License for more details.
+
+    You should have received a copy of the GNU General Public License
+    along with LOOT.  If not, see
+    <https://www.gnu.org/licenses/>.
+    */
+
+#ifndef LOOT_API_SORTING_GROUP_SORT
+#define LOOT_API_SORTING_GROUP_SORT
+
+#include <string>
+#include <unordered_map>
+#include <unordered_set>
+
+#include "loot/metadata/group.h"
+
+namespace loot {
+// Map entries are a group name and names of transitive load after groups.
+std::unordered_map<std::string, std::unordered_set<std::string>> GetTransitiveAfterGroups(const std::unordered_set<Group> groups);
+}
+#endif
diff --git a/src/tests/api/internals/main.cpp b/src/tests/api/internals/main.cpp
index c9bd6c1b..c8ccf9e0 100644
--- a/src/tests/api/internals/main.cpp
+++ b/src/tests/api/internals/main.cpp
@@ -45,6 +45,7 @@
 #include "tests/api/internals/metadata/priority_test.h"
 #include "tests/api/internals/metadata/tag_test.h"
 #include "tests/api/internals/metadata_list_test.h"
+#include "tests/api/internals/sorting/group_sort_test.h"
 #include "tests/api/internals/sorting/plugin_sorter_test.h"
 #include "tests/api/internals/plugin_test.h"
 
diff --git a/src/tests/api/internals/sorting/group_sort_test.h b/src/tests/api/internals/sorting/group_sort_test.h
new file mode 100644
index 00000000..ffd8144c
--- /dev/null
+++ b/src/tests/api/internals/sorting/group_sort_test.h
@@ -0,0 +1,70 @@
+/*  LOOT
+
+A load order optimisation tool for Oblivion, Skyrim, Fallout 3 and
+Fallout: New Vegas.
+
+Copyright (C) 2018    WrinklyNinja
+
+This file is part of LOOT.
+
+LOOT is free software: you can redistribute
+it and/or modify it under the terms of the GNU General Public License
+as published by the Free Software Foundation, either version 3 of
+the License, or (at your option) any later version.
+
+LOOT is distributed in the hope that it will
+be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of
+MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+GNU General Public License for more details.
+
+You should have received a copy of the GNU General Public License
+along with LOOT.  If not, see
+<https://www.gnu.org/licenses/>.
+*/
+
+#ifndef LOOT_TESTS_API_INTERNALS_SORTING_GROUP_SORT_TEST
+#define LOOT_TESTS_API_INTERNALS_SORTING_GROUP_SORT_TEST
+
+#include "api/sorting/group_sort.h"
+
+#include <gtest/gtest.h>
+
+#include "loot/exception/cyclic_interaction_error.h"
+
+namespace loot {
+namespace test {
+TEST(GetTransitiveAfterGroups, shouldMapGroupsToTheirTransitiveAfterGroups) {
+  std::unordered_set<Group> groups({
+    Group("a"),
+    Group("b", std::unordered_set<std::string>({ "a" })),
+    Group("c", std::unordered_set<std::string>({ "b" }))
+  });
+
+  auto mapped = GetTransitiveAfterGroups(groups);
+
+  EXPECT_TRUE(mapped["a"].empty());
+  EXPECT_EQ(std::unordered_set<std::string>({ "a" }), mapped["b"]);
+  EXPECT_EQ(std::unordered_set<std::string>({ "a", "b" }), mapped["c"]);
+}
+
+TEST(GetTransitiveAfterGroups, shouldThrowIfAnAfterGroupDoesNotExist) {
+  std::unordered_set<Group> groups({
+    Group("b", std::unordered_set<std::string>({ "a" }))
+  });
+
+  EXPECT_THROW(GetTransitiveAfterGroups(groups), std::invalid_argument);
+}
+
+TEST(GetTransitiveAfterGroups, shouldThrowIfAfterGroupsAreCyclic) {
+  std::unordered_set<Group> groups({
+    Group("a", std::unordered_set<std::string>({ "c" })),
+    Group("b", std::unordered_set<std::string>({ "a" })),
+    Group("c", std::unordered_set<std::string>({ "b" }))
+  });
+
+  EXPECT_THROW(GetTransitiveAfterGroups(groups), CyclicInteractionError);
+}
+}
+}
+
+#endif