This study examines three core processes in undergraduates' reasoning about four different evidence types (i.e., anecdotal, observational, correlational, and causal). In particular, we examine undergraduates' processes of evidence identification, evaluation, and selection of evidence to include in writing and how these manifest across different evidence types. Undergraduates' justifications for their evidence evaluations and selections were also examined. Results showed that students were successfully able to differentiate anecdotal evidence from other types of quantitative evidence and rated anecdotal evidence as least convincing. At the same time, we found that undergraduates were not able to differentiate among the other three types of evidence (i.e., descriptive/observational, correlational, causal) effectively. Moreover, a variety of criteria were identified in undergraduates' justifications for evidence evaluation and selection. Undergraduates commonly evaluated evidence based on its essential features as well as the methods used for its collection, although justifications differed across evidence types. Undergraduates also commonly considered its essential features when selecting evidence to include in writing. At the same time, undergraduates frequently mismatched the type of evidence provided (e.g., correlational) and its essential characteristics (e.g., describing it as causal). Future directions and instructional implications are discussed.