diff --git a/cranelift/docs/langref.rst b/cranelift/docs/langref.rst
index ad2ccb4299..845bc4da37 100644
--- a/cranelift/docs/langref.rst
+++ b/cranelift/docs/langref.rst
@@ -200,6 +200,18 @@ in this reference.
 
     Either :type:`bool` or :type:`iN`.
 
+Immediate operand types
+-----------------------
+
+These types are not part of the normal SSA type system. They are used to
+indicate the different kinds of immediate operands on an instruction.
+
+.. type:: imm64
+
+    A 64-bit immediate integer. The value of this operand is interpreted as a
+    signed two's complement integer. Instruction encodings may limit the valid
+    range.
+
 Control flow
 ============
 
diff --git a/cranelift/docs/metaref.rst b/cranelift/docs/metaref.rst
index 7a8c156142..b4dda9576d 100644
--- a/cranelift/docs/metaref.rst
+++ b/cranelift/docs/metaref.rst
@@ -38,13 +38,28 @@ Predefined types
 .. automodule:: cretonne.types
     :members:
 
+.. currentmodule:: cretonne
+
 Parametric polymorphism
 -----------------------
-.. currentmodule:: cretonne
 
 Instruction operands can be defined with *type variables* instead of concrete
 types for their operands. This makes the instructions polymorphic.
 
 .. autoclass:: TypeVar
 
+Immediates
+----------
 
+Immediate instruction operands don't correspond to SSA values, but have values
+that are encoded directly in the instruction. Immediate operands don't
+have types from the :class:`cretonne.Type` type system; they often have
+enumerated values of a specific type. The type of an immediate operand is
+indicated with an instance of :class:`ImmediateType`.
+
+.. autoclass:: ImmediateType
+
+.. automodule:: cretonne.immediates
+    :members:
+
+.. currentmodule:: cretonne
diff --git a/meta/cretonne/__init__.py b/meta/cretonne/__init__.py
index e8cdfe3f55..60c3748106 100644
--- a/meta/cretonne/__init__.py
+++ b/meta/cretonne/__init__.py
@@ -110,3 +110,23 @@ class TypeVar(object):
     def __init__(self, name):
         self.name = name
 
+#
+# Immediate operands.
+#
+# Instances of immediate operand types are provided in the cretonne.immediates
+# module.
+
+class ImmediateType(object):
+    """
+    The type of an immediate instruction operand.
+    """
+
+    def __init__(self, name, doc):
+        self.name = name
+        self.__doc__ = doc
+
+    def __str__(self):
+        return self.name
+
+    def __repr__(self):
+        return 'ImmediateType({})'.format(self.name)
diff --git a/meta/cretonne/immediates.py b/meta/cretonne/immediates.py
new file mode 100644
index 0000000000..6b499d5215
--- /dev/null
+++ b/meta/cretonne/immediates.py
@@ -0,0 +1,12 @@
+"""
+The cretonne.immdiates module predefines all the Cretonne immediate operand
+types.
+"""
+
+from . import ImmediateType
+
+#: A 64-bit immediate integer operand.
+#:
+#: This type of immediate integer can interact with SSA values with any
+#: :py:class:`cretonne.IntType` type.
+imm64 = ImmediateType('imm64', 'A 64-bit immediate integer.')