Flow cytometry is a flexible and useful tool in the armamentarium of translational and basic researchers. Based on a microfluidic system that has roots in the 1930s, flow cytometry allows for the multi-parametric analysis of samples on a single cell basis in a high-throughput manner. Flow cytometry has paved the way for multiple advancements in the field of cytometry including the development of cytometry by time of flight (CyTOF). CyTOF allows for higher-dimensional analysis of samples on a single-cell basis with over 100 parameters. Clinically, flow and mass cytometry have been frequently used in oncology and immunology. Research applications include a wide variety of uses including phenotyping, cell death and proliferation, cell signalling, fluorescence-activated cell sorting, monitoring immune responses, pharmacokinetics, and evaluating the proteomics landscape of a cell. This chapter describes the fundamentals of flow and mass cytometry for the surgeon scientist.