The incidence of fungal infections is increasing as the population at risk expands. Cost, resistance, and morbidity and mortality are key issues. Adding to the antifungal armamentarium is necessary to address these therapeutic dilemmas. Caspofungin is the first member of a new class of antifungal agents, the echinocandins, to be approved for clinical use. Caspofungin is classified as a glucan synthase inhibitor and represents a class of agents with a novel mechanism of action. Unlike currently available agents (polyenes, pyrimidines, azoles) that exert their effect on the fungal cell membrane, the echinocandins are the first agents to inhibit fungal cell wall synthesis. Caspofungin exhibits activity against Aspergillus spp. and Candida spp., including non-albicans species. Data from clinical trials demonstrate that caspofungin is effective in patients with invasive aspergillosis as well as candida esophagitis. Its Food and Drug Administration-approved indication is limited to invasive aspergillosis refractory to or intolerant of current therapy.