Lawyers who represent or litigate against government agencies must wrestle so frequently with the concept of agency "discretion" that they may be forgiven for believing that the term is devoid of intrinsic meaning—a chameleon deriving substance only from its particular context. For instance, mandamus will lie only for ministerial acts, as opposed to "discretionary" ones. Agency acts that are "by law committed to agency discretion" are not reviewable in court under the federal Administrative Procedure Act (APA). However, agency actions are reviewed for "abuse of discretion." On the other hand, tort suits against the government will not be allowed for exercises of "discretionary functions," and individual government officials may be absolutely immune from tort suits only for exercises of "discretionary" duties. Because courts making these determinations do not always use the same criteria, it is easy to conclude that there is no consistent definition of "discretion" that will contribute to sound analysis in each context. Such a definitional analysis is suggested here. The approach will be inductive-to set forth an analysis and then to see if it works satisfactorily. The test will be whether the definitions comport with sound case law while furthering the policy reasons for the use of the concept of discretion in each particular context.