A highly detailed program listing for the Logic Theory Machine (LT), a computer program written in Information Processing Language-V (IPL-V), and developed especially for use as a pedagogical model. The text portions expand on the documentation in the listing, tracing program flow, analyzing routines used, and providing insight into the structure and development of the program. LT was originally programmed in an early version of IPL to derive proofs of logic expressions in the sentential calculus of Whitehead and Russell. In rewriting it for use as a teaching aid, a new method of replacement on sub-expressions has been included, and many minor changes effecting improvements in clarity have been incorporated. Features of the code that were unjustifiably hard to explain have been simplified. LT can be implemented on any computer for which an IPL-V processor is available.