diff --git a/lib/cretonne/src/entity_ref.rs b/lib/cretonne/src/entity/mod.rs
similarity index 91%
rename from lib/cretonne/src/entity_ref.rs
rename to lib/cretonne/src/entity/mod.rs
index 9990b521f0..26c1e54353 100644
--- a/lib/cretonne/src/entity_ref.rs
+++ b/lib/cretonne/src/entity/mod.rs
@@ -2,6 +2,8 @@
 //!
 //! This module defines an `EntityRef` trait that should be implemented by reference types wrapping
 //! a small integer index.
+//!
+//! Various data structures based on the entity references are defined in sub-modules.
 
 /// A type wrapping a small integer index should implement `EntityRef` so it can be used as the key
 /// of an `EntityMap` or `SparseMap`.
@@ -19,7 +21,7 @@ pub trait EntityRef: Copy + Eq {
 macro_rules! entity_impl {
     // Basic traits.
     ($entity:ident) => {
-        impl $crate::entity_ref::EntityRef for $entity {
+        impl $crate::entity::EntityRef for $entity {
             fn new(index: usize) -> Self {
                 assert!(index < (::std::u32::MAX as usize));
                 $entity(index as u32)
diff --git a/lib/cretonne/src/entity_list.rs b/lib/cretonne/src/entity_list.rs
index 4b535e3f56..3685f00eab 100644
--- a/lib/cretonne/src/entity_list.rs
+++ b/lib/cretonne/src/entity_list.rs
@@ -46,7 +46,7 @@
 //! The index stored in an `EntityList` points to part 2, the list elements. The value 0 is
 //! reserved for the empty list which isn't allocated in the vector.
 
-use entity_ref::EntityRef;
+use entity::EntityRef;
 use std::hash::{Hash, Hasher};
 use std::marker::PhantomData;
 use std::mem;
@@ -483,7 +483,7 @@ mod tests {
     use super::*;
     use super::{sclass_size, sclass_for_length};
     use ir::Inst;
-    use entity_ref::EntityRef;
+    use entity::EntityRef;
 
     #[test]
     fn size_classes() {
diff --git a/lib/cretonne/src/entity_map.rs b/lib/cretonne/src/entity_map.rs
index be73b790e1..7afb863ed0 100644
--- a/lib/cretonne/src/entity_map.rs
+++ b/lib/cretonne/src/entity_map.rs
@@ -9,7 +9,7 @@
 //! - A *secondary* `EntityMap` contains additional data about entities kept in a primary map. The
 //!   values need to implement `Clone + Default` traits so the map can be grown with `ensure`.
 
-use entity_ref::EntityRef;
+use entity::EntityRef;
 use std::marker::PhantomData;
 use std::ops::{Index, IndexMut};
 
diff --git a/lib/cretonne/src/ir/jumptable.rs b/lib/cretonne/src/ir/jumptable.rs
index aaaa694a50..c0f97afea3 100644
--- a/lib/cretonne/src/ir/jumptable.rs
+++ b/lib/cretonne/src/ir/jumptable.rs
@@ -122,7 +122,7 @@ impl Display for JumpTableData {
 mod tests {
     use super::JumpTableData;
     use ir::Ebb;
-    use entity_ref::EntityRef;
+    use entity::EntityRef;
 
     #[test]
     fn empty() {
diff --git a/lib/cretonne/src/ir/layout.rs b/lib/cretonne/src/ir/layout.rs
index 3f31d34f23..9e03daa8a9 100644
--- a/lib/cretonne/src/ir/layout.rs
+++ b/lib/cretonne/src/ir/layout.rs
@@ -1086,7 +1086,7 @@ impl<'c, 'fc: 'c, 'fd> InstInserterBase<'fd> for LayoutCursorInserter<'c, 'fc, '
 #[cfg(test)]
 mod tests {
     use super::{Layout, Cursor, CursorBase, CursorPosition};
-    use entity_ref::EntityRef;
+    use entity::EntityRef;
     use ir::{Ebb, Inst, ProgramOrder};
     use std::cmp::Ordering;
 
diff --git a/lib/cretonne/src/ir/progpoint.rs b/lib/cretonne/src/ir/progpoint.rs
index 7adeb43c5c..7d6e9197bd 100644
--- a/lib/cretonne/src/ir/progpoint.rs
+++ b/lib/cretonne/src/ir/progpoint.rs
@@ -1,6 +1,6 @@
 //! Program points.
 
-use entity_ref::EntityRef;
+use entity::EntityRef;
 use ir::{Ebb, Inst, ValueDef};
 use std::fmt;
 use std::u32;
@@ -135,7 +135,7 @@ pub trait ProgramOrder {
 #[cfg(test)]
 mod tests {
     use super::*;
-    use entity_ref::EntityRef;
+    use entity::EntityRef;
     use ir::{Inst, Ebb};
 
     #[test]
diff --git a/lib/cretonne/src/isa/registers.rs b/lib/cretonne/src/isa/registers.rs
index 2823fbea37..eacce024fb 100644
--- a/lib/cretonne/src/isa/registers.rs
+++ b/lib/cretonne/src/isa/registers.rs
@@ -1,6 +1,6 @@
 //! Data structures describing the registers in an ISA.
 
-use entity_ref::EntityRef;
+use entity::EntityRef;
 use std::fmt;
 
 /// Register units are the smallest units of register allocation.
diff --git a/lib/cretonne/src/lib.rs b/lib/cretonne/src/lib.rs
index b021bf55b2..324698c53c 100644
--- a/lib/cretonne/src/lib.rs
+++ b/lib/cretonne/src/lib.rs
@@ -13,7 +13,7 @@ pub const VERSION: &'static str = env!("CARGO_PKG_VERSION");
 #[macro_use]
 pub mod dbg;
 #[macro_use]
-pub mod entity_ref;
+pub mod entity;
 
 pub mod binemit;
 pub mod bitset;
diff --git a/lib/cretonne/src/regalloc/diversion.rs b/lib/cretonne/src/regalloc/diversion.rs
index 4f17d3685d..bbc5c067ae 100644
--- a/lib/cretonne/src/regalloc/diversion.rs
+++ b/lib/cretonne/src/regalloc/diversion.rs
@@ -104,7 +104,7 @@ impl RegDiversions {
 mod tests {
     use super::*;
     use ir::Value;
-    use entity_ref::EntityRef;
+    use entity::EntityRef;
 
     #[test]
     fn inserts() {
diff --git a/lib/cretonne/src/regalloc/liverange.rs b/lib/cretonne/src/regalloc/liverange.rs
index 9174e0cdba..6b5353910e 100644
--- a/lib/cretonne/src/regalloc/liverange.rs
+++ b/lib/cretonne/src/regalloc/liverange.rs
@@ -435,7 +435,7 @@ impl SparseMapValue<Value> for LiveRange {
 mod tests {
     use super::LiveRange;
     use ir::{Inst, Ebb, Value};
-    use entity_ref::EntityRef;
+    use entity::EntityRef;
     use ir::{ProgramOrder, ExpandedProgramPoint};
     use std::cmp::Ordering;
 
diff --git a/lib/cretonne/src/regalloc/solver.rs b/lib/cretonne/src/regalloc/solver.rs
index ea028f551b..4cec792afe 100644
--- a/lib/cretonne/src/regalloc/solver.rs
+++ b/lib/cretonne/src/regalloc/solver.rs
@@ -702,7 +702,7 @@ impl Solver {
 #[cfg(test)]
 #[cfg(build_arm32)]
 mod tests {
-    use entity_ref::EntityRef;
+    use entity::EntityRef;
     use ir::Value;
     use isa::{TargetIsa, RegClass, RegUnit};
     use regalloc::AllocatableSet;
diff --git a/lib/cretonne/src/sparse_map.rs b/lib/cretonne/src/sparse_map.rs
index c1a8bf5480..84c17f7b5f 100644
--- a/lib/cretonne/src/sparse_map.rs
+++ b/lib/cretonne/src/sparse_map.rs
@@ -36,7 +36,7 @@
 //!   contain their own key.
 
 use entity_map::EntityMap;
-use entity_ref::EntityRef;
+use entity::EntityRef;
 use std::mem;
 use std::slice;
 use std::u32;
@@ -221,7 +221,7 @@ pub type SparseSet<T> = SparseMap<T, T>;
 #[cfg(test)]
 mod tests {
     use super::*;
-    use entity_ref::EntityRef;
+    use entity::EntityRef;
     use ir::Inst;
 
     // Mock key-value object for testing.
diff --git a/lib/frontend/src/frontend.rs b/lib/frontend/src/frontend.rs
index d81cee4bc7..935251e89e 100644
--- a/lib/frontend/src/frontend.rs
+++ b/lib/frontend/src/frontend.rs
@@ -7,7 +7,7 @@ use cretonne::ir::function::DisplayFunction;
 use cretonne::isa::TargetIsa;
 use ssa::{SSABuilder, SideEffects, Block};
 use cretonne::entity_map::{EntityMap, PrimaryEntityData};
-use cretonne::entity_ref::EntityRef;
+use cretonne::entity::EntityRef;
 use std::hash::Hash;
 
 /// Permanent structure used for translating into Cretonne IL.
@@ -571,7 +571,7 @@ impl<'a, Variable> FunctionBuilder<'a, Variable>
 #[cfg(test)]
 mod tests {
 
-    use cretonne::entity_ref::EntityRef;
+    use cretonne::entity::EntityRef;
     use cretonne::ir::{FunctionName, Function, CallConv, Signature, ArgumentType, InstBuilder};
     use cretonne::ir::types::*;
     use frontend::{ILBuilder, FunctionBuilder};
diff --git a/lib/frontend/src/lib.rs b/lib/frontend/src/lib.rs
index 10a06b23cc..69723ae50c 100644
--- a/lib/frontend/src/lib.rs
+++ b/lib/frontend/src/lib.rs
@@ -35,7 +35,7 @@
 //! extern crate cretonne;
 //! extern crate cton_frontend;
 //!
-//! use cretonne::entity_ref::EntityRef;
+//! use cretonne::entity::EntityRef;
 //! use cretonne::ir::{FunctionName, CallConv, Function, Signature, ArgumentType, InstBuilder};
 //! use cretonne::ir::types::*;
 //! use cton_frontend::{ILBuilder, FunctionBuilder};
diff --git a/lib/frontend/src/ssa.rs b/lib/frontend/src/ssa.rs
index fc5c85f1dd..bad49c6264 100644
--- a/lib/frontend/src/ssa.rs
+++ b/lib/frontend/src/ssa.rs
@@ -10,7 +10,7 @@ use cretonne::ir::{Ebb, Value, Inst, Type, DataFlowGraph, JumpTables, Layout, Cu
 use cretonne::ir::instructions::BranchInfo;
 use std::hash::Hash;
 use cretonne::entity_map::{EntityMap, PrimaryEntityData};
-use cretonne::entity_ref::EntityRef;
+use cretonne::entity::EntityRef;
 use cretonne::packed_option::PackedOption;
 use cretonne::packed_option::ReservedValue;
 use std::u32;
@@ -607,7 +607,7 @@ impl<Variable> SSABuilder<Variable>
 
 #[cfg(test)]
 mod tests {
-    use cretonne::entity_ref::EntityRef;
+    use cretonne::entity::EntityRef;
     use cretonne::ir::{Function, InstBuilder, Cursor, CursorBase, Inst, JumpTableData};
     use cretonne::ir::types::*;
     use cretonne::verify_function;
diff --git a/lib/reader/src/sourcemap.rs b/lib/reader/src/sourcemap.rs
index b085a78c1b..cfd7e85cec 100644
--- a/lib/reader/src/sourcemap.rs
+++ b/lib/reader/src/sourcemap.rs
@@ -7,7 +7,7 @@
 //! The `SourceMap` struct defined in this module makes the same mapping available to parser
 //! clients.
 
-use cretonne::entity_ref::EntityRef;
+use cretonne::entity::EntityRef;
 use cretonne::ir::entities::AnyEntity;
 use cretonne::ir::{StackSlot, GlobalVar, JumpTable, Ebb, Value, SigRef, FuncRef};
 use error::{Result, Location};