Macroinvertebrates constitute the backbone of megafaunal communities in benthic ecosystems around the globe. Many macroinvertebrates have vital roles in benthic ecosystems, ranging from enhancing habitat complexity to providing staple food sources for other organisms. Regardless of how familiar macroinvertebrates are to the general public, very few studies have attempted to describe benthic macroinvertebrate assemblages across large spatial scale in the continental shelf waters of the Pacific Northwest. This study describes different subtidal macroinvertebrate assemblages off Washington and Oregon based on species-substrata associations and the key species that distinguish one assemblage from another. Two data sets were used for this study: underwater footage collected by the submersible Delta during 1993-1995 geological surveys, and footage collected by the remotely operated vehicle (ROV) Hammerhead during macroinvertebrate surveys in late summer 2011. Footages from these surveys were used to document species-substrata associations and distinguish different assemblages based on species composition similarities and dissimilarities. In addition, I determined if a specific group of invertebrates, Asteroids (Echinodermata), were useful in explaining different assemblage patterns, after all other environmental parameters were taken into account. Findings of this study can be used not only to shed light on the structure of macroinvertebrate communities in the Pacific Northwest, but also as baseline data for future research on the direct and indirect effects of potential offshore installations on macroinvertebrate communities across the continental shelf waters. / Graduation date: 2012