Because these objects represent pieces of CLOS programs, and because their behavior provides the behavior of the CLOS language itself, they are considered meta-level objects or metaobjects. The protocol followed by the metaobjects to provide the behavior of CLOS is called the CLOS Metaobject Protocol (MOP).
- As of 15 October 2017, a modern public domain online version of AMOP chapters 5 and 6 (MOP specification) is available.
- A hypertext version of the The Common Lisp Object System MetaObject Protocol (copyrighted, no modifications allowed)
- An alternative hypertext version of The Metaobject Protocol of the Common Lisp Object System, made by Robert Strandh (public domain)
- The MOP-standards-discussion for suggestions on MOP 2.0
- The MOP design patterns for some common patterns while using the MOP
- Open Implementations and Metaobject Protocols by Gregor Kiczales and Andreas Paepcke (recommended by Paolo Amoroso on comp.lang.lisp)
- AMOP - AMOP is an acronym used in reference to the book The Art of the Metaobject Protocol, by Gregor Kiczales, and which was published by MIT Press, 1991
- C3 superclass linearization MRO - The C3 Method Resolution Order from A Monotonic Superclass Linearization for Dylan (1996) is increasingly popular
- Closer to MOP - Closer to MOP is a compatibility layer that rectifies many of the absent or incorrect MOP features as detected by MOP Feature Tests
- fare-mop - fare-mop has a few simple utilities relying on the MOP
- MOP design patterns - How to add your own default class for metaclass instances by Pascal Costanza
- MOP-standards-discussion - The MOP is great, but nothing is perfect
- mop-utils - MOP-utils is a small library of utilities for the MetaObject Protocol
- Portable CommonLoops - Portable CommonLoops is a reference CLOS/MOP implementation originally developed by Xerox, deriving from the Loops Project