To systematically improve the appropriateness of antibiotic prescribing, antimicrobial stewardship programs have been developed. There is a paucity of literature examining how pharmacists perform antimicrobial stewardship using a clinical decision support system in a hospital setting. The purpose of this qualitative study was to develop a model exploring how pharmacists perform antimicrobial stewardship to identify areas for programmatic improvement. Semistructured interviews were conducted across a health care system until saturation of themes was reached. Pharmacists identified that self-efficacy and time were vital for antimicrobial stewardship to be performed, while culture of the hospital and attitude facilitated the process of stewardship. Antimicrobial stewardship programs using clinical decision support tools should ensure pharmacists have adequate time to address rules, provide easy-to-use resources and training to support self-efficacy, and engage influential physicians to support a culture of collaboration.