Flow cytometry provides many advantages including single-cell quantitative analysis, high sample throughput, and multiplex cell characterization. This seminar will provide an overview of powerful methods to study cell function using flow cytometry. Discussion will include a variety of probes and assays for cell cycle, proliferation, and senescence. Additionally, we will discuss fluorescence-based sensors for viability, apoptosis, cytotoxicity, and hypoxia. These methods will be demonstrated with model systems focused on cancer immunotherapy, drug screening, and primary cells.