Regression testing is a necessary but expensive activity aimed at showing that code has not been adversely affected by changes. A selective approach to regression testing attempts to reuse tests from an existing test suite to test a modified program. This paper outlines issues relevant to selective retest approaches, and presents a framework within which such approaches can be evaluated. This framework is then used to evaluate and compare existing selective retest algorithms. The evaluation reveals strengths and weaknesses of existing methods, and highlights problems that future work in this area should address.