diff --git a/include/openmc/cross_sections.h b/include/openmc/cross_sections.h
index 72e89692c4..d8a3799c58 100644
--- a/include/openmc/cross_sections.h
+++ b/include/openmc/cross_sections.h
@@ -30,24 +30,36 @@ public:
   }
 
   // Data members
-  Type type_;
-  std::vector<std::string> materials_;
-  std::string path_;
+  Type type_; //!< Type of data library
+  std::vector<std::string> materials_; //!< Materials contained in library
+  std::string path_; //!< File path to library
 };
 
+using LibraryKey = std::pair<Library::Type, std::string>;
+
 //==============================================================================
 // Global variable declarations
 //==============================================================================
 
+namespace data {
+
+//!< Data libraries
 extern std::vector<Library> libraries;
-using LibraryKey = std::pair<Library::Type, std::string>;
-extern std::map<LibraryKey, std::size_t> library_dict;
+
+//! Maps (type, name) to index in libraries
+extern std::map<LibraryKey, std::size_t> library_map;
+
+} // namespace data
 
 //==============================================================================
 // Non-member functions
 //==============================================================================
 
+//! Read cross sections file (either XML or multigroup H5) and populate data
+//! libraries
 extern "C" void read_cross_sections_xml();
+
+//! Read cross_sections.xml and populate data libraries
 void read_ce_cross_sections_xml();
 
 } // namespace openmc
diff --git a/src/cross_sections.cpp b/src/cross_sections.cpp
index ebe9dc0e7e..aca46a5b9a 100644
--- a/src/cross_sections.cpp
+++ b/src/cross_sections.cpp
@@ -19,10 +19,12 @@ namespace openmc {
 // Global variable declarations
 //==============================================================================
 
-std::vector<Library> libraries;
-std::map<LibraryKey, std::size_t> library_dict;
+namespace data {
 
-extern "C" void read_mg_cross_sections_header();
+std::vector<Library> libraries;
+std::map<LibraryKey, std::size_t> library_map;
+
+}
 
 //==============================================================================
 // Library methods
@@ -76,6 +78,8 @@ Library::Library(pugi::xml_node node, const std::string& directory)
 // Non-member functions
 //==============================================================================
 
+extern "C" void read_mg_cross_sections_header();
+
 void read_cross_sections_xml()
 {
   // Check if materials.xml exists
@@ -146,12 +150,12 @@ void read_cross_sections_xml()
 
   // Establish mapping between (type, material) and index in libraries
   int i = 0;
-  for (const auto& lib : libraries) {
+  for (const auto& lib : data::libraries) {
     for (const auto& name : lib.materials_) {
       std::string lower_name = name;
       to_lower(lower_name);
       LibraryKey key {lib.type_, lower_name};
-      library_dict.insert({key, i});
+      data::library_map.insert({key, i});
     }
     ++i;
   }
@@ -161,7 +165,7 @@ void read_cross_sections_xml()
     std::string lower_name = name;
     to_lower(lower_name);
     LibraryKey key {Library::Type::neutron, lower_name};
-    if (library_dict.find(key) == library_dict.end()) {
+    if (data::library_map.find(key) == data::library_map.end()) {
       fatal_error("Could not find resonant scatterer " +
         name + " in cross_sections.xml file!");
     }
@@ -200,11 +204,11 @@ void read_ce_cross_sections_xml()
   }
 
   for (const auto& node_library : root.children("library")) {
-    libraries.emplace_back(node_library, directory);
+    data::libraries.emplace_back(node_library, directory);
   }
 
   // Make sure file was not empty
-  if (libraries.empty()) {
+  if (data::libraries.empty()) {
     fatal_error("No cross section libraries present in cross_sections.xml file.");
   }
 }
@@ -214,25 +218,25 @@ void read_ce_cross_sections_xml()
 //==============================================================================
 
 extern "C" void library_clear() {
-  libraries.clear();
-  library_dict.clear();
+  data::libraries.clear();
+  data::library_map.clear();
 }
 
 extern "C" const char* library_path(int type, const char* name) {
   auto lib_type = static_cast<Library::Type>(type);
   LibraryKey key {lib_type, name};
-  if (library_dict.find(key) == library_dict.end()) {
+  if (data::library_map.find(key) == data::library_map.end()) {
     return nullptr;
   } else {
-    auto idx = library_dict[key];
-    return libraries[idx].path_.c_str();
+    auto idx = data::library_map[key];
+    return data::libraries[idx].path_.c_str();
   }
 }
 
 extern "C" bool library_present(int type, const char* name) {
   auto lib_type = static_cast<Library::Type>(type);
   LibraryKey key {lib_type, name};
-  return library_dict.find(key) != library_dict.end();
+  return data::library_map.find(key) != data::library_map.end();
 }
 
 } // namespace openmc
diff --git a/src/mgxs_interface.cpp b/src/mgxs_interface.cpp
index 9b320c4e1c..80aa66621c 100644
--- a/src/mgxs_interface.cpp
+++ b/src/mgxs_interface.cpp
@@ -122,7 +122,7 @@ void read_mg_cross_sections_header_c(hid_t file_id)
     Library lib {};
     lib.type_ = Library::Type::neutron;
     lib.materials_.push_back(name);
-    libraries.push_back(lib);
+    data::libraries.push_back(lib);
   }
 }