A taxonomic key, diagnoses, and geographic distributions are provided for the 24 species of harvestmen that are known from or are likely to occur in Maryland. Twenty species are documented, with records of Caddo agilis, Phalangium opilio, Odiellus pictus, Leiobunum flavum, and Vonones sayi published for the first time. Four additional species— Acropsopilio boopis, Crosbycus dasycnemus, Leiobunum cretatum, and Sabacon cavicolens—are expected to occur in Maryland but have yet to be recorded. Due to misidentifications or other taxonomic issues, 2 species (Hadrobunus grandis and Leiobunum crassipalpe) have been reported erroneously from the state and another (L. speciosum) may be a color variant of a widespread species, L. vittatum. Additional species may yet emerge, primarily through new systematic analyses or unanticipated range extensions of known taxa. The key uses many new characteristics, including those that substantially improve the identification of females. Information on the collection, preservation, rearing, dissection, and identification of harvestmen is summarized.