Microplastics (MP) are ubiquitous in our environment and pose one of the biggest emerging threats to the global environmental community. The science surrounding MP, their potential health effects, and knowledge of their fate and transport is very new and ongoing, with research articles being published at a rapidly accelerating rate. Even techniques and best practices for sample collection and analysis of these tiny particles and fibers are still very much evolving. ITRC's Microplastics Team has synthesized the available information on MP into a single comprehensive guidance document.