Index: clangd/index/FileIndex.h
===================================================================
--- clangd/index/FileIndex.h
+++ clangd/index/FileIndex.h
@@ -73,6 +73,10 @@
   void lookup(const LookupRequest &Req,
               llvm::function_ref<void(const Symbol &)> Callback) const override;
 
+
+  void findOccurrences(const OccurrencesRequest &Req,
+                       llvm::function_ref<void(const SymbolOccurrence &)>
+                           Callback) const override;
 private:
   FileSymbols FSymbols;
   MemIndex Index;
Index: clangd/index/FileIndex.cpp
===================================================================
--- clangd/index/FileIndex.cpp
+++ clangd/index/FileIndex.cpp
@@ -9,6 +9,7 @@
 
 #include "FileIndex.h"
 #include "SymbolCollector.h"
+#include "../Logger.h"
 #include "clang/Index/IndexingAction.h"
 #include "clang/Lex/Preprocessor.h"
 
@@ -105,5 +106,11 @@
   Index.lookup(Req, Callback);
 }
 
+void FileIndex::findOccurrences(
+    const OccurrencesRequest &Req,
+    llvm::function_ref<void(const SymbolOccurrence &)> Callback) const {
+  log("findOccurrences is not implemented.");
+}
+
 } // namespace clangd
 } // namespace clang
Index: clangd/index/Index.h
===================================================================
--- clangd/index/Index.h
+++ clangd/index/Index.h
@@ -280,6 +280,40 @@
   std::vector<Symbol> Symbols;  // Sorted by SymbolID to allow lookup.
 };
 
+// Describes the kind of a symbol occurrence.
+//
+// This is a bitfield which can be combined from different kinds.
+enum class SymbolOccurrenceKind : uint8_t {
+  Unknown = 0,
+  Declaration = static_cast<uint8_t>(index::SymbolRole::Declaration),
+  Definition = static_cast<uint8_t>(index::SymbolRole::Definition),
+  Reference = static_cast<uint8_t>(index::SymbolRole::Reference),
+};
+inline SymbolOccurrenceKind operator|(SymbolOccurrenceKind L,
+                                      SymbolOccurrenceKind R) {
+  return static_cast<SymbolOccurrenceKind>(static_cast<uint8_t>(L) |
+                                           static_cast<uint8_t>(R));
+}
+inline SymbolOccurrenceKind &operator|=(SymbolOccurrenceKind &L,
+                                        SymbolOccurrenceKind R) {
+  return L = L | R;
+}
+inline SymbolOccurrenceKind operator&(SymbolOccurrenceKind A,
+                                      SymbolOccurrenceKind B) {
+  return static_cast<SymbolOccurrenceKind>(static_cast<uint8_t>(A) &
+                                           static_cast<uint8_t>(B));
+}
+
+// Represents a symbol occurrence in the source file. It could be a
+// declaration/definition/reference occurrence.
+//
+// WARNING: Location does not own the underlying data - Copies are shallow.
+struct SymbolOccurrence {
+  // The location of the occurrence.
+  SymbolLocation Location;
+  SymbolOccurrenceKind Kind;
+};
+
 struct FuzzyFindRequest {
   /// \brief A query string for the fuzzy find. This is matched against symbols'
   /// un-qualified identifiers and should not contain qualifiers like "::".
@@ -305,6 +339,11 @@
   llvm::DenseSet<SymbolID> IDs;
 };
 
+struct OccurrencesRequest {
+  llvm::DenseSet<SymbolID> IDs;
+  SymbolOccurrenceKind Filter;
+};
+
 /// \brief Interface for symbol indexes that can be used for searching or
 /// matching symbols among a set of symbols based on names or unique IDs.
 class SymbolIndex {
@@ -327,8 +366,15 @@
   lookup(const LookupRequest &Req,
          llvm::function_ref<void(const Symbol &)> Callback) const = 0;
 
-  // FIXME: add interfaces for more index use cases:
-  //  - getAllOccurrences(SymbolID);
+  /// CrossReference finds all symbol occurrences (e.g. references,
+  /// declarations, definitions) and applies \p Callback on each result.
+  ///
+  /// Resutls are returned in arbitrary order.
+  ///
+  /// The returned result must be deep-copied if it's used outside Callback.
+  virtual void findOccurrences(
+      const OccurrencesRequest &Req,
+      llvm::function_ref<void(const SymbolOccurrence &)> Callback) const = 0;
 };
 
 } // namespace clangd
Index: clangd/index/MemIndex.h
===================================================================
--- clangd/index/MemIndex.h
+++ clangd/index/MemIndex.h
@@ -31,10 +31,14 @@
   fuzzyFind(const FuzzyFindRequest &Req,
             llvm::function_ref<void(const Symbol &)> Callback) const override;
 
-  virtual void
+  void
   lookup(const LookupRequest &Req,
          llvm::function_ref<void(const Symbol &)> Callback) const override;
 
+  void findOccurrences(const OccurrencesRequest &Req,
+                       llvm::function_ref<void(const SymbolOccurrence &)>
+                           Callback) const override;
+
 private:
   std::shared_ptr<std::vector<const Symbol *>> Symbols;
   // Index is a set of symbols that are deduplicated by symbol IDs.
Index: clangd/index/MemIndex.cpp
===================================================================
--- clangd/index/MemIndex.cpp
+++ clangd/index/MemIndex.cpp
@@ -87,5 +87,11 @@
   return std::move(MemIdx);
 }
 
+void MemIndex::findOccurrences(
+    const OccurrencesRequest &Req,
+    llvm::function_ref<void(const SymbolOccurrence &)> Callback) const {
+  log("findOccurrences is not implemented.");
+}
+
 } // namespace clangd
 } // namespace clang
Index: clangd/index/Merge.cpp
===================================================================
--- clangd/index/Merge.cpp
+++ clangd/index/Merge.cpp
@@ -7,6 +7,7 @@
 //
 //===---------------------------------------------------------------------===//
 #include "Merge.h"
+#include "../Logger.h"
 #include "llvm/ADT/STLExtras.h"
 #include "llvm/Support/raw_ostream.h"
 namespace clang {
@@ -74,6 +75,12 @@
         Callback(*Sym);
   }
 
+  void findOccurrences(const OccurrencesRequest &Req,
+                       llvm::function_ref<void(const SymbolOccurrence &)>
+                           Callback) const override {
+    log("findOccurrences is not implemented.");
+  }
+
 private:
   const SymbolIndex *Dynamic, *Static;
 };
Index: unittests/clangd/CodeCompleteTests.cpp
===================================================================
--- unittests/clangd/CodeCompleteTests.cpp
+++ unittests/clangd/CodeCompleteTests.cpp
@@ -893,6 +893,10 @@
   void lookup(const LookupRequest &,
               llvm::function_ref<void(const Symbol &)>) const override {}
 
+  void findOccurrences(const OccurrencesRequest &Req,
+                       llvm::function_ref<void(const SymbolOccurrence &)>
+                           Callback) const override {}
+
   const std::vector<FuzzyFindRequest> allRequests() const { return Requests; }
 
 private: