Flow cytometry is a technology that simultaneously measures and then analyses multiple physical characteristics of individual cells, as they flow in a fluid stream through one or more laser beams.

The cell’s relative size, relative internal complexity or granularity, and relative fluorescence intensity are the properties measured by a flow cytometer. These characteristics are determined using an optical-to-electronic coupling system that records how the cell scatters incident laser light and emits fluorescence. Once the data is collected, it can be displayed as graphics or histograms, and statistics can be generated.

A common application of flow cytometry is the assessment of cell surface receptor expression, also known as immunophenotyping.