There is considerable disagreement among researchers regarding the defining attributes of biodata items, especially in contrast to other self-report measures. This paper provides a conceptual rationale for the use of biodata in order to evaluate various proposed attributes of biodata, and to clarify similarities and differences between biodata and temperament items. It is suggested that the core attribute of biodata items is that the items pertain to historical events that may have shaped the person's behavior and identity. Other attributes advanced as antidotes to socially desirable responding and faking are that biodata items reflect external events, that they be limited to objective and first-hand recollections, that they be potentially verifiable, and that they measure discrete, unique events when appropriate. Some researchers also require that the life events being sampled be controllable and equally accessible to all respondents. Items may also need to be visibly job relevant and nonintrusive to avoid legal censure. Disagreements among researchers regarding the importance of these attributes are discussed, and implications for practice and research are proposed.