diff --git a/lib/cretonne/meta/cretonne/__init__.py b/lib/cretonne/meta/cretonne/__init__.py
index a8865e1966..6672d6d869 100644
--- a/lib/cretonne/meta/cretonne/__init__.py
+++ b/lib/cretonne/meta/cretonne/__init__.py
@@ -707,6 +707,11 @@ class InstructionFormat(object):
             self.members.append(member)
             yield k
 
+    def __str__(self):
+        args = ', '.join('{}: {}'.format(m, k) if m else str(k)
+                         for m, k in zip(self.members, self.kinds))
+        return '{}({})'.format(self.name, args)
+
     def __getattr__(self, attr):
         # type: (str) -> FormatField
         """
diff --git a/lib/cretonne/meta/gen_instr.py b/lib/cretonne/meta/gen_instr.py
index 8a7e813223..bb14d36375 100644
--- a/lib/cretonne/meta/gen_instr.py
+++ b/lib/cretonne/meta/gen_instr.py
@@ -19,6 +19,7 @@ def gen_formats(fmt):
     fmt.line('#[derive(Copy, Clone, PartialEq, Eq, Debug)]')
     with fmt.indented('pub enum InstructionFormat {', '}'):
         for f in cretonne.InstructionFormat.all_formats:
+            fmt.doc_comment(str(f))
             fmt.line(f.name + ',')
     fmt.line()
 
@@ -172,6 +173,7 @@ def gen_opcodes(groups, fmt):
     fmt.line('#[derive(Copy, Clone, PartialEq, Eq, Debug)]')
     instrs = []
     with fmt.indented('pub enum Opcode {', '}'):
+        fmt.doc_comment('An invalid opcode.')
         fmt.line('NotAnOpcode,')
         for g in groups:
             for i in g.instructions:
@@ -364,6 +366,7 @@ def gen_format_constructor(iform, fmt):
     proto = '{}({})'.format(iform.name, ', '.join(args))
     proto += " -> (Inst, &'f mut DataFlowGraph)"
 
+    fmt.doc_comment(str(iform))
     fmt.line('#[allow(non_snake_case)]')
     with fmt.indented('fn {} {{'.format(proto), '}'):
         # Generate the instruction data.
diff --git a/lib/cretonne/meta/gen_settings.py b/lib/cretonne/meta/gen_settings.py
index c3c4710ea3..8e35d05909 100644
--- a/lib/cretonne/meta/gen_settings.py
+++ b/lib/cretonne/meta/gen_settings.py
@@ -16,10 +16,12 @@ def gen_enum_types(sgrp, fmt):
         if not isinstance(setting, EnumSetting):
             continue
         ty = camel_case(setting.name)
+        fmt.doc_comment('Values for {}.'.format(setting))
         fmt.line('#[derive(Debug, PartialEq, Eq)]')
-        fmt.line(
-                'pub enum {} {{ {} }}'
-                .format(ty, ", ".join(camel_case(v) for v in setting.values)))
+        with fmt.indented('pub enum {} {{'.format(ty), '}'):
+            for v in setting.values:
+                fmt.doc_comment('`{}`.'.format(v))
+                fmt.line(camel_case(v) + ',')
 
 
 def gen_getter(setting, sgrp, fmt):
@@ -70,7 +72,7 @@ def gen_getters(sgrp, fmt):
     """
     fmt.doc_comment("User-defined settings.")
     with fmt.indented('impl Flags {', '}'):
-        # Dynamic numbered predicate getter.
+        fmt.doc_comment('Dynamic numbered predicate getter.')
         with fmt.indented(
                 'pub fn numbered_predicate(&self, p: usize) -> bool {', '}'):
             fmt.line(
@@ -187,6 +189,7 @@ def gen_constructor(sgrp, parent, fmt):
         if sgrp.parent:
             p = sgrp.parent
             args = '{}: &{}::Flags, {}'.format(p.name, p.qual_mod, args)
+        fmt.doc_comment('Create flags {} settings group.'.format(sgrp.name))
         with fmt.indented(
                 'pub fn new({}) -> Flags {{'.format(args), '}'):
             fmt.line('let bvec = builder.state_for("{}");'.format(sgrp.name))
diff --git a/lib/cretonne/src/cfg.rs b/lib/cretonne/src/cfg.rs
index 76ccc27965..f68d8bcbf4 100644
--- a/lib/cretonne/src/cfg.rs
+++ b/lib/cretonne/src/cfg.rs
@@ -33,19 +33,12 @@ pub type BasicBlock = (Ebb, Inst);
 /// A container for the successors and predecessors of some Ebb.
 #[derive(Debug, Clone, Default)]
 pub struct CFGNode {
+    /// EBBs that are the targets of branches and jumps in this EBB.
     pub successors: Vec<Ebb>,
+    /// Basic blocks that can branch or jump to this EBB.
     pub predecessors: Vec<BasicBlock>,
 }
 
-impl CFGNode {
-    pub fn new() -> CFGNode {
-        CFGNode {
-            successors: Vec::new(),
-            predecessors: Vec::new(),
-        }
-    }
-}
-
 /// The Control Flow Graph maintains a mapping of ebbs to their predecessors
 /// and successors where predecessors are basic blocks and successors are
 /// extended basic blocks.
@@ -88,10 +81,12 @@ impl ControlFlowGraph {
         self.data[to].predecessors.push(from);
     }
 
+    /// Get the CFG predecessor basic blocks to `ebb`.
     pub fn get_predecessors(&self, ebb: Ebb) -> &Vec<BasicBlock> {
         &self.data[ebb].predecessors
     }
 
+    /// Get the CFG successors to `ebb`.
     pub fn get_successors(&self, ebb: Ebb) -> &Vec<Ebb> {
         &self.data[ebb].successors
     }
diff --git a/lib/cretonne/src/dominator_tree.rs b/lib/cretonne/src/dominator_tree.rs
index c81e579f6b..e331f5657b 100644
--- a/lib/cretonne/src/dominator_tree.rs
+++ b/lib/cretonne/src/dominator_tree.rs
@@ -1,10 +1,11 @@
-/// ! A Dominator Tree represented as mappings of Ebbs to their immediate dominator.
+//! A Dominator Tree represented as mappings of Ebbs to their immediate dominator.
 
 use cfg::*;
 use ir::Ebb;
 use ir::entities::NO_INST;
 use entity_map::EntityMap;
 
+/// The dominator tree for a single function.
 pub struct DominatorTree {
     data: EntityMap<Ebb, Option<BasicBlock>>,
 }
diff --git a/lib/cretonne/src/ir/condcodes.rs b/lib/cretonne/src/ir/condcodes.rs
index 692ecda96f..dfa6b054f5 100644
--- a/lib/cretonne/src/ir/condcodes.rs
+++ b/lib/cretonne/src/ir/condcodes.rs
@@ -29,15 +29,25 @@ pub trait CondCode: Copy {
 /// difference.
 #[derive(Clone, Copy, PartialEq, Eq, Debug)]
 pub enum IntCC {
+    /// `==`.
     Equal,
+    /// `!=`.
     NotEqual,
+    /// Signed `<`.
     SignedLessThan,
+    /// Signed `>=`.
     SignedGreaterThanOrEqual,
+    /// Signed `>`.
     SignedGreaterThan,
+    /// Signed `<=`.
     SignedLessThanOrEqual,
+    /// Unsigned `<`.
     UnsignedLessThan,
+    /// Unsigned `>=`.
     UnsignedGreaterThanOrEqual,
+    /// Unsigned `>`.
     UnsignedGreaterThan,
+    /// Unsigned `<=`.
     UnsignedLessThanOrEqual,
 }
 
@@ -131,24 +141,38 @@ impl FromStr for IntCC {
 /// except the impossible `!UN & !EQ & !LT & !GT` and the always true `UN | EQ | LT | GT`.
 #[derive(Clone, Copy, PartialEq, Eq, Debug)]
 pub enum FloatCC {
-    Ordered, // EQ | LT | GT
-    Unordered, // UN
+    /// EQ | LT | GT
+    Ordered,
+    /// UN
+    Unordered,
 
-    Equal, // EQ
-    // The C '!=' operator is the inverse of '==': NotEqual.
-    NotEqual, // UN | LT | GT
-    OrderedNotEqual, // LT | GT
-    UnorderedOrEqual, // UN | EQ
+    /// EQ
+    Equal,
+    /// The C '!=' operator is the inverse of '==': `NotEqual`.
+    /// UN | LT | GT
+    NotEqual,
+    /// LT | GT
+    OrderedNotEqual,
+    /// UN | EQ
+    UnorderedOrEqual,
 
-    LessThan, // LT
-    LessThanOrEqual, // LT | EQ
-    GreaterThan, // GT
-    GreaterThanOrEqual, // GT | EQ
+    /// LT
+    LessThan,
+    /// LT | EQ
+    LessThanOrEqual,
+    /// GT
+    GreaterThan,
+    /// GT | EQ
+    GreaterThanOrEqual,
 
-    UnorderedOrLessThan, // UN | LT
-    UnorderedOrLessThanOrEqual, // UN | LT | EQ
-    UnorderedOrGreaterThan, // UN | GT
-    UnorderedOrGreaterThanOrEqual, // UN | GT | EQ
+    /// UN | LT
+    UnorderedOrLessThan,
+    /// UN | LT | EQ
+    UnorderedOrLessThanOrEqual,
+    /// UN | GT
+    UnorderedOrGreaterThan,
+    /// UN | GT | EQ
+    UnorderedOrGreaterThanOrEqual,
 }
 
 impl CondCode for FloatCC {
diff --git a/lib/cretonne/src/ir/entities.rs b/lib/cretonne/src/ir/entities.rs
index bd8913e5bf..384e4d3ae9 100644
--- a/lib/cretonne/src/ir/entities.rs
+++ b/lib/cretonne/src/ir/entities.rs
@@ -98,16 +98,16 @@ impl Default for Inst {
 #[derive(Copy, Clone, PartialEq, Eq, Hash, Debug)]
 pub struct Value(u32);
 
-// Value references can either reference an instruction directly, or they can refer to the extended
-// value table.
+/// Value references can either reference an instruction directly, or they can refer to the
+/// extended value table.
 pub enum ExpandedValue {
-    // This is the first value produced by the referenced instruction.
+    /// This is the first value produced by the referenced instruction.
     Direct(Inst),
 
-    // This value is described in the extended value table.
+    /// This value is described in the extended value table.
     Table(usize),
 
-    // This is NO_VALUE.
+    /// This is NO_VALUE.
     None,
 }
 
@@ -135,19 +135,23 @@ impl Value {
             None
         }
     }
+    /// Create a `Direct` value corresponding to the first value produced by `i`.
     pub fn new_direct(i: Inst) -> Value {
         let encoding = i.index() * 2;
         assert!(encoding < u32::MAX as usize);
         Value(encoding as u32)
     }
 
+    /// Create a `Table` value referring to entry `i` in the `DataFlowGraph.extended_values` table.
+    /// This constructor should not be used directly. Use the public `DataFlowGraph` methods to
+    /// manipulate values.
     pub fn new_table(index: usize) -> Value {
         let encoding = index * 2 + 1;
         assert!(encoding < u32::MAX as usize);
         Value(encoding as u32)
     }
 
-    // Expand the internal representation into something useful.
+    /// Expand the internal representation into something useful.
     pub fn expand(&self) -> ExpandedValue {
         use self::ExpandedValue::*;
         if *self == NO_VALUE {
@@ -312,12 +316,19 @@ impl Default for SigRef {
 pub enum AnyEntity {
     /// The whole function.
     Function,
+    /// An extended basic block.
     Ebb(Ebb),
+    /// An instruction.
     Inst(Inst),
+    /// An SSA value.
     Value(Value),
+    /// A stack slot.
     StackSlot(StackSlot),
+    /// A jump table.
     JumpTable(JumpTable),
+    /// An external function.
     FuncRef(FuncRef),
+    /// A function call signature.
     SigRef(SigRef),
 }
 
diff --git a/lib/cretonne/src/ir/extfunc.rs b/lib/cretonne/src/ir/extfunc.rs
index 6f89d5d307..a47ff4ad7a 100644
--- a/lib/cretonne/src/ir/extfunc.rs
+++ b/lib/cretonne/src/ir/extfunc.rs
@@ -14,11 +14,14 @@ use ir::{Type, FunctionName, SigRef};
 /// details that are needed to call a function correctly.
 #[derive(Clone, PartialEq, Eq, Debug)]
 pub struct Signature {
+    /// Types of the arguments passed to the function.
     pub argument_types: Vec<ArgumentType>,
+    /// Types returned from the function.
     pub return_types: Vec<ArgumentType>,
 }
 
 impl Signature {
+    /// Create a new blank signature.
     pub fn new() -> Signature {
         Signature {
             argument_types: Vec::new(),
@@ -59,13 +62,16 @@ impl Display for Signature {
 /// how the argument is passed.
 #[derive(Copy, Clone, PartialEq, Eq, Debug)]
 pub struct ArgumentType {
+    /// Type of the argument value.
     pub value_type: Type,
+    /// Method for extending argument to a full register.
     pub extension: ArgumentExtension,
     /// Place this argument in a register if possible.
     pub inreg: bool,
 }
 
 impl ArgumentType {
+    /// Create an argument type with default flags.
     pub fn new(vt: Type) -> ArgumentType {
         ArgumentType {
             value_type: vt,
@@ -109,7 +115,9 @@ pub enum ArgumentExtension {
 /// Information about a function that can be called directly with a direct `call` instruction.
 #[derive(Clone, Debug)]
 pub struct ExtFuncData {
+    /// Name of the external function.
     pub name: FunctionName,
+    /// Call signature of function.
     pub signature: SigRef,
 }
 
diff --git a/lib/cretonne/src/ir/funcname.rs b/lib/cretonne/src/ir/funcname.rs
index 0f6f106365..d84b25ac2b 100644
--- a/lib/cretonne/src/ir/funcname.rs
+++ b/lib/cretonne/src/ir/funcname.rs
@@ -14,6 +14,7 @@ use std::ascii::AsciiExt;
 pub struct FunctionName(String);
 
 impl FunctionName {
+    /// Create new function name equal to `s`.
     pub fn new<S: Into<String>>(s: S) -> FunctionName {
         FunctionName(s.into())
     }
diff --git a/lib/cretonne/src/ir/immediates.rs b/lib/cretonne/src/ir/immediates.rs
index 0395d13f26..e2fc0c446d 100644
--- a/lib/cretonne/src/ir/immediates.rs
+++ b/lib/cretonne/src/ir/immediates.rs
@@ -17,6 +17,7 @@ use std::str::FromStr;
 pub struct Imm64(i64);
 
 impl Imm64 {
+    /// Create a new `Imm64` representing the signed number `x`.
     pub fn new(x: i64) -> Imm64 {
         Imm64(x)
     }
@@ -374,6 +375,7 @@ fn parse_float(s: &str, w: u8, t: u8) -> Result<u64, &'static str> {
 }
 
 impl Ieee32 {
+    /// Create a new `Ieee32` representing the number `x`.
     pub fn new(x: f32) -> Ieee32 {
         Ieee32(x)
     }
@@ -403,6 +405,7 @@ impl FromStr for Ieee32 {
 }
 
 impl Ieee64 {
+    /// Create a new `Ieee64` representing the number `x`.
     pub fn new(x: f64) -> Ieee64 {
         Ieee64(x)
     }
diff --git a/lib/cretonne/src/ir/instructions.rs b/lib/cretonne/src/ir/instructions.rs
index 103dcd4fe5..f601169beb 100644
--- a/lib/cretonne/src/ir/instructions.rs
+++ b/lib/cretonne/src/ir/instructions.rs
@@ -93,6 +93,7 @@ impl FromStr for Opcode {
 /// 16 bytes on 64-bit architectures. If more space is needed to represent an instruction, use a
 /// `Box<AuxData>` to store the additional information out of line.
 #[derive(Clone, Debug)]
+#[allow(missing_docs)]
 pub enum InstructionData {
     Nullary { opcode: Opcode, ty: Type },
     Unary {
@@ -226,14 +227,17 @@ pub enum InstructionData {
 pub struct VariableArgs(Vec<Value>);
 
 impl VariableArgs {
+    /// Create an empty argument list.
     pub fn new() -> VariableArgs {
         VariableArgs(Vec::new())
     }
 
+    /// Add an argument to the end.
     pub fn push(&mut self, v: Value) {
         self.0.push(v)
     }
 
+    /// Check if the list is empty.
     pub fn is_empty(&self) -> bool {
         self.0.is_empty()
     }
@@ -276,6 +280,7 @@ impl Default for VariableArgs {
 /// Payload data for `vconst`.
 #[derive(Clone, Debug)]
 pub struct UnaryImmVectorData {
+    /// Raw vector data.
     pub imm: ImmVector,
 }
 
@@ -292,6 +297,7 @@ impl Display for UnaryImmVectorData {
 /// Payload data for ternary instructions with multiple results, such as `iadd_carry`.
 #[derive(Clone, Debug)]
 pub struct TernaryOverflowData {
+    /// Value arguments.
     pub args: [Value; 3],
 }
 
@@ -305,7 +311,9 @@ impl Display for TernaryOverflowData {
 /// in the allowed InstructionData size.
 #[derive(Clone, Debug)]
 pub struct JumpData {
+    /// Jump destination EBB.
     pub destination: Ebb,
+    /// Arguments passed to destination EBB.
     pub varargs: VariableArgs,
 }
 
@@ -323,8 +331,11 @@ impl Display for JumpData {
 /// in the allowed InstructionData size.
 #[derive(Clone, Debug)]
 pub struct BranchData {
+    /// Value argument controlling the branch.
     pub arg: Value,
+    /// Branch destination EBB.
     pub destination: Ebb,
+    /// Arguments passed to destination EBB.
     pub varargs: VariableArgs,
 }
 
@@ -353,6 +364,8 @@ pub struct CallData {
 pub struct IndirectCallData {
     /// Callee function.
     pub arg: Value,
+
+    /// Signature of the callee function.
     pub sig_ref: SigRef,
 
     /// Dynamically sized array containing call argument values.
@@ -362,7 +375,7 @@ pub struct IndirectCallData {
 /// Payload of a return instruction.
 #[derive(Clone, Debug)]
 pub struct ReturnData {
-    // Dynamically sized array containing return values.
+    /// Dynamically sized array containing return values.
     pub varargs: VariableArgs,
 }
 
diff --git a/lib/cretonne/src/isa/mod.rs b/lib/cretonne/src/isa/mod.rs
index 67d5a91c29..5705fe3a55 100644
--- a/lib/cretonne/src/isa/mod.rs
+++ b/lib/cretonne/src/isa/mod.rs
@@ -87,6 +87,7 @@ impl settings::Configurable for Builder {
     }
 }
 
+/// Methods that are specialized to a target ISA.
 pub trait TargetIsa {
     /// Get the name of this ISA.
     fn name(&self) -> &'static str;
diff --git a/lib/cretonne/src/isa/riscv/mod.rs b/lib/cretonne/src/isa/riscv/mod.rs
index cdc49f6973..06a9c890d0 100644
--- a/lib/cretonne/src/isa/riscv/mod.rs
+++ b/lib/cretonne/src/isa/riscv/mod.rs
@@ -16,6 +16,7 @@ struct Isa {
     cpumode: &'static [shared_enc_tables::Level1Entry<u16>],
 }
 
+/// Get an ISA builder for creating RISC-V targets.
 pub fn isa_builder() -> IsaBuilder {
     IsaBuilder {
         setup: settings::builder(),
diff --git a/lib/cretonne/src/lib.rs b/lib/cretonne/src/lib.rs
index ae25157248..aef83bd433 100644
--- a/lib/cretonne/src/lib.rs
+++ b/lib/cretonne/src/lib.rs
@@ -1,14 +1,12 @@
+//! Cretonne code generation library.
 
-// ====------------------------------------------------------------------------------------==== //
-//
-// Cretonne code generation library.
-//
-// ====------------------------------------------------------------------------------------==== //
+#![deny(missing_docs)]
 
 pub use verifier::verify_function;
 pub use write::write_function;
 pub use legalizer::legalize_function;
 
+/// Version number of the cretonne crate.
 pub const VERSION: &'static str = env!("CARGO_PKG_VERSION");
 
 pub mod ir;
diff --git a/lib/cretonne/src/settings.rs b/lib/cretonne/src/settings.rs
index 37d09d2ba8..291211b1b3 100644
--- a/lib/cretonne/src/settings.rs
+++ b/lib/cretonne/src/settings.rs
@@ -144,6 +144,7 @@ pub enum Error {
     BadValue,
 }
 
+/// A result returned when changing a setting.
 pub type Result<T> = result::Result<T, Error>;
 
 /// Implementation details for generated code.
@@ -156,10 +157,15 @@ pub mod detail {
 
     /// An instruction group template.
     pub struct Template {
+        /// Name of the instruction group.
         pub name: &'static str,
+        /// List of setting descriptors.
         pub descriptors: &'static [Descriptor],
+        /// Union of all enumerators.
         pub enumerators: &'static [&'static str],
+        /// Hash table of settings.
         pub hash_table: &'static [u16],
+        /// Default values.
         pub defaults: &'static [u8],
     }
 
@@ -227,7 +233,10 @@ pub mod detail {
     #[derive(Clone, Copy)]
     pub enum Detail {
         /// A boolean setting only uses one bit, numbered from LSB.
-        Bool { bit: u8 },
+        Bool {
+            /// 0-7.
+            bit: u8,
+        },
 
         /// A numerical setting uses the whole byte.
         Num,
diff --git a/lib/cretonne/src/verifier.rs b/lib/cretonne/src/verifier.rs
index 2b544967e2..9e044a738a 100644
--- a/lib/cretonne/src/verifier.rs
+++ b/lib/cretonne/src/verifier.rs
@@ -61,7 +61,9 @@ use std::result;
 /// A verifier error.
 #[derive(Debug, PartialEq, Eq)]
 pub struct Error {
+    /// The entity causing the verifier error.
     pub location: AnyEntity,
+    /// Error message.
     pub message: String,
 }
 
@@ -71,6 +73,7 @@ impl Display for Error {
     }
 }
 
+/// Verifier result.
 pub type Result<T> = result::Result<T, Error>;
 
 // Create an `Err` variant of `Result<X>` from a location and `format!` args.
@@ -90,11 +93,12 @@ macro_rules! err {
     };
 }
 
+/// Verify `func`.
 pub fn verify_function(func: &Function) -> Result<()> {
     Verifier::new(func).run()
 }
 
-pub struct Verifier<'a> {
+struct Verifier<'a> {
     func: &'a Function,
 }
 
@@ -165,7 +169,7 @@ impl<'a> Verifier<'a> {
 
 #[cfg(test)]
 mod tests {
-    use super::*;
+    use super::{Verifier, Error};
     use ir::Function;
     use ir::instructions::{InstructionData, Opcode};
     use ir::types;