The object oriented programming style used in the Smalltalk and Actor languages is available in Lisp Machine Lisp, and used by the Lisp Machine software system. It is used to perform generic operations on objects. Part of its implementation is simply a convention in procedure calling style; part is a powerful language feature, called Flavors, for defining abstract objects. This chapter attempts to explain what programming the objects and with message passing means, the various means of implementing these in Lisp Machine Lisp, and when you should use them. It assumes no prior knowledge of any other language.