A fully illustrated key is presented for identifying genera of oribatid mites known from or suspected of occurring in the Pacific Northwest. The manual includes an introduction detailing sampling methodology; an illustrated glossary of all terminology used; two color plates of all taxa from the H.J. Andrews Experimental Forest; a diagramatic key to the 16 major groups of adult oribatids; illustrations to aid in quick recognition of the 16 adult groups; keys to all adult genera; and a diagramatic key to the major types of immature oribatid mites with local species illustrated. The text on adults is broken into 16 sections, each structured around a key to the genera within each major type of oribatid mite; the text associated with the keys describes each species from the Andrews Forest, its microhabitat preference, pattern of abundance, and seasonal phenology. A total of 246 scanning electron micrographs (with pointers indicating characters useful for identification) are provided to help in identifying species.