Flow cytometry is a biophysical technology that simultaneously measures and then analyzes multiple physical characteristics of up to thousands of cells per second, as they flow in a fluid stream exposed to a beam of light. In order to do so, a flow cytometer is made up of three main systems: fluidics, optics, and electronics.

Flow cytometry has many applications in life sciences, such as cell counting, cell sorting, biomarker detection, and protein engineering. In the recent years, all flow cytometers are able to sort cells and, therefore, when researchers use it for that purpose the technique is also called Fluorescence-activated cell sorting (FACS).