Pharmacy managers often must justify clinical pharmacy services (CPSs). This can be done by generalizing evidence from the literature or by conducting local evaluations. In either case, it is important that the clinical, humanistic or economic benefits of CPSs are considered, and limitations of the studies recognized. The basic model for the evaluation of CPSs includes the consideration of costs and outcomes, as well as the inclusion of a comparator group. Recent systematic reviews and individual studies provide good evidence regarding the value of CPSs, and are discussed here. Benefit-to-cost ratios of selected CPSs are also provided. While much of the evidence for CPSs has been conducted in the hospital setting, in the future, CPS expansion will occur in ambulatory care settings and will be benefited by healthcare reform efforts.