We present a systematic literature review of the prior work on Undergraduate Teaching Assistants (UTAs) in Computer Science with two goals: (1) to create a taxonomy of practices that relate to the design and implementation of UTA programs, (2) to identify the benefits of using UTAs as claimed by the literature and characterize the level of evidence for those claims. We analyze 336 excerpts from 40 papers related to these goals. We use content analysis on excerpts describing practices to extract high-level themes that include recruiting, UTA and program coordinator duties, training, evaluation and organization of UTA programs. We perform a more fine-grained analysis within each theme to identify specific questions about UTA programs and the answers provided by the literature. Using a similar technique, we report on the claimed benefits of UTA programs to students, UTAs, instructors and institutions. Our analysis follows well-defined protocols involving multiple reviewers and we report on the inter-rater reliability. The results provided in this paper lay the groundwork for developing evidence-based best practices in UTA programs and inform practice and policy related to the use of UTAs at tertiary institutions. As such, it is relevant to educators establishing a new UTA program, expanding an existing program, or continuously improving an established program, as well as those designing research studies of such programs.