Plastics could be one of the most important environmental problems our society will face this century. The continuous and increasing production of these synthetic materials and the lack of an appropriate plastic waste management approach are intensifying the plastic contamination of water bodies worldwide, as well as land and air. The fact that plastics break down into smaller particles (micro- and nanoplastics) by the action of physical and chemical reactions and do not degrade biologically is a cause of concern as plastics are believed to cause harm in animals, plants, and humans. From sampling to identification, several techniques have been developed to determine the type of plastics found in aquatic environments. Following the sampling process of a water body, using nets, pumps, or other devices, depending on the sample type, it is usually necessary to treat the samples for separation and purification purposes. The next step is the use of analytical methods to identify the synthetic pollutants. The most common approaches are microscopy, spectroscopy, and thermal analysis. This Review summarizes the most important technologies applied to analyze the importance of plastics as a contaminant in water bodies, offering an excellent compendium regarding the sampling, separation, purification, and identification of micro- and nanoplastics in aqueous samples, including an overview of notable articles that have utilized these approaches successfully.