This is the first comprehensive monograph of the introduced and cryptogenic marine and estuarine organisms of the Hawaiian Archipelago, from the island of Hawaii to Kure and Midway Atolls, between the latitudes of 19N and 29N. Covered are protoctists, fungi, invertebrates, fish, algae, and flowering plants, inhabiting coastal environments influenced by the sea. The habitats covered are the supralittoral zone (supporting "strand" or "maritime" species), the intertidal zone, and the sublittoral (subtidal), including non-native parasites, commensals, or other symbionts. 490 species are treated, of which 301 are introduced and 117 are cryptogenic. The rest of the species are either of unknown establishments, species that escaped or were intentionally released but did not establish, species that were unintentionally introduced but failed to establish, intercepted species, species that represent doubtful or erroneous records, native species previously treated as introduced, waifs, or species that are of uncertain presence in marine waters.