The ever-increasing use of engineered nanomaterials will lead to heightened levels of these materials in the environment. The present review aims to provide a comprehensive overview of current knowledge regarding nanoparticle transport and aggregation in aquatic environments. Nanoparticle aggregation and deposition behavior will dictate particle transport potential and thus the environmental fate and potential ecotoxicological impacts of these materials. In this review, colloidal forces governing nanoparticle deposition and aggregation are outlined. Essential equations used to assess particle-particle and particle-surface interactions, along with Hamaker constants for specific nanoparticles and the attributes exclusive to nanoscale particle interactions, are described. Theoretical and experimental approaches for evaluating nanoparticle aggregation and deposition are presented, and the major findings of laboratory studies examining these processes are also summarized. Finally, we describe some of the challenges encountered when attempting to quantify the transport of nanoparticles in aquatic environments.