In biotechnology, flow cytometry is a laser- or impedance-based, biophysical technology that is widely used in cell counting, cell sorting, biomarker detection and protein engineering, by suspending cells in a stream of fluid and passing them through an electronic detection apparatus. A flow cytometer provides simultaneous multiparametric analysis of the physical and chemical characteristics of up to thousands of particles per second.

Flow cytometry is routinely used in the diagnosis of health disorders, especially blood cancers, but has many other applications in basic research, clinical practice and clinical trials. A common variation involves linking the analytical capability of the flow cytometer to a sorting device, to physically separate and thereby purify particles of interest based on their optical properties. Such a process is called cell sorting, and the instrument is commonly termed a cell sorter.