This Chapter provides insight into the physical, hydrodynamic and biochemical processes governing the transport of microplastics in estuarine environments. The focus is mainly on the physical and hydrodynamical processes that control microplastic transport, although the role of biochemical processes on their dynamical behaviour is discussed. The chapter begins by describing the microplastic physical properties and their variability with the time spent in the environment due to weathering, biofouling, and flocculation. This variability makes them different from other suspended particulate matter and critically affects their buoyancy, deposition and erosion rates. The more prominent hydrodynamic processes driving the transport of microplastics are then discussed. Next, four case studies are presented to illustrate microplastic dynamics in different types of estuaries, from well-mixed to strongly stratified. Finally, sampling and numerical approaches for analysing the dispersion of microplastics in estuaries are reviewed.