The Pacific Ocean is the most expansive geographical feature on Earth. Included in its domain are thousands of atolls, smaller islands and, depending on how its boundaries are defined, several larger islands and island groups. Members of the grass family, Poaceae, are almost ubiquitous and are widespread across the Pacific. This detailed key enumerates 420 species of non-bambusoid grasses in 120 genera and provides a taxonomic reference for grasses growing throughout this region.