Microplastics pollution of terrestrial and marine environmental compartments is an issue of concern worldwide, but information on the key sources, pathways, distribution, and impacts is still scarce in many cases, fragmentary at best, and typically difficult to compare owing to a lack of harmonization in methodologies. In this chapter, we present the latest evidence of microplastics as a global threat, together with current knowledge gaps, the challenges associated with establishing a global monitoring system and what legislative framework might be needed for their control. The chapter will also describe the complexity of this environmental problem, highlighting the key reasons for why regulation at the local, regional, and global levels is currently limited and discussing possible ways forward.