The cell membrane-coated nanoparticle is a biomimetic platform consisting of a nanoparticulate core coated with membrane derived from a cell, such as a red blood cell, platelet, or cancer cell. The cell membrane "disguise" allows the particles to be perceived by the body as the source cell by interacting with its surroundings using the translocated surface membrane components. The newly bestowed characteristics of the membrane-coated nanoparticle can be utilized for biological interfacing in the body, providing natural solutions to many biomedical issues. This Review will cover the interactions of these cell membrane-coated nanoparticles and their applications within three biomedical areas of interest, including (i) drug delivery, (ii) detoxification, and (iii) immune modulation.