Since their ubiquity in the ocean and marine organisms was first revealed, global concern about microplastics has grown considerably. The North Pacific Ocean and the adjacent marginal seas have high levels of microplastic contamination compared with the global average. This special issue on microplastics was organized by the North Pacific Marine Science Organization to share information on microplastic pollution in the North Pacific region. The special issue highlights high levels of contamination in the North Pacific both on shorelines and at the sea surface. Particularly high levels of contamination were reported on the western and southern coasts of Korea. Sources, including sewage discharge, aquaculture, and shipyards, were implicated. With the direction and energy of surface winds and currents have an important influence on shoreline patterns of distribution. The special issue also demonstrates potential for ingestion of microplastic by small planktonic organisms at the base of the food chain. A wide range of chemicals are associated with plastic debris and concerns are expressed about the potential for these chemicals to transfer to biota upon ingestion. As an introduction to the topic, this paper provides a brief background on microplastic contamination, highlights some key research gaps, and summarizes findings from the articles published in this issue.