One method for producing verified implementations of programming languages is to formally derive them from abstract machines. Tail-recursive abstract machines provide e#cient support for iterative processes via the ordinary procedure call mechanism. This document argues that the use of tail-recursive abstract machines incurs only a small increase in theorem-proving burden when compared with what is required when using ordinary abstract machines. The position is supported by comparing correctness proofs performed using the BoyerMoore theorem prover. A by-product of this e#ort is a syntactic criterion based on tail contexts for identifying which procedure calls must be implemented as tail calls. The concept of tail contexts was used in the latest Scheme Report, the only language specification known to the author that defines the requirement that its implementations must be tail recursive. Keywords: tail recursion, tail call, SECD machine, CEK machine, verified implementati...