Given the ubiquity of microplastics in the environment, how much microplastic do people and other living things take in? Microplastics can be taken into organisms or generated internally by ingestion, inhalation, or skin exposure; once inside an organism, microplastics can be taken into cells by translocation, or by endocytosis. Dosage data on microplastics is limited. Mussels, for example, may contribute up to 5 g of microplastics per week to the diet of each shellfish consumer, while 1800-10,000 plastic microparticles per person may be consumed with seafood annually. In a year, a consumer may take in 160,000-1,000,000 microplastic particles from tap water and 533 g of microplastics from salt; the particles are predominantly polyethylene, polypropylene, and poly(ethylene terephthalate). Overall, 39,000-52,000 microplastic particles a year were estimated to be consumed per person with food, both from the food itself and from particles deposited from the air onto plates and silverware. Another estimate was that an average person ingests 14-714 mg of microplastics per day. Through simulation, it has been estimated that about 100,000 microplastic particles per person could be inhaled annually. While their use has been banned in many countries, up to 2.4 mg/d of microplastic particles in soap may be taken in through the skin. The amount of microplastic present in the food we eat, the water we drink, and in the air we breathe is important for understanding how much microplastic we take in, but microplastics taken into an organism may not be retained and thus may not be present to exert their biological effects. Knowing how microplastics are taken into and retained by tissues is thus critical for assessing their impact on human health. Microplastic particle entry may occur directly from the gastrointestinal (GI) tract, by endocytosis either through the lungs (with 78-200 m particles) or through Peyer's patches in the GI tract (patches of lymphoid cells in the small intestine which mediate the development of immune responses to ingested proteins), by phagocytosis through the lungs (for 1-3 m particles), or by persorption (kneading particles through gaps between epithelial cells). In mice, 28-50% of the 100 nm poly(lactate-glycolate) particles administered were taken up by mice from oral administration, while 0.01-7.5% of 1 m and 10 m particles were internalized (primarily through the Peyer's patches in their intestinal tracts). The size, surface functionalization, charge, and protein adsorption to microplastic particles are important in how the particles are retained or eliminated by organisms. Microplastics may be removed from organisms by transfer to bile, urine, exhalations, cerebrospinal fluid, and breast milk. In mussels, 10 m polystyrene nanoparticles entered circulation from the gut. When 200 g of starch particles were given to people, the particles were observed in a variety of body fluids, but only 0.002% of the particles were found in blood after 24 h. As noted in mice, the bioavailability of microplastics likely depends strongly on particle size. Microplastics may be removed from organisms by transfer to bile, urine, exhalations, cerebrospinal fluid, and breast milk. In mussels, 10 m polystyrene nanoparticles entered circulation from the gut. In mice, 28-50% of the 100 nm poly(lactate-glycolate) particles administered were taken up by mice from oral administration, while 0.01-7.5% of 1 m and 10 m particles were internalized (primarily through the Peyer's patches in their intestinal tracts). When 200 g of starch particles were given to people, the particles were observed in a variety of body fluids, but only 0.002% of the particles were found in blood after 24 h. As noted in mice, the bioavailability of microplastics likely depends strongly on particle size.