There has been increasing recognition of the importance of metabolism on immune cell differentiation, homeostasis, and function. Recently, our lab and others have begun to investigate the metabolic requirements for NK cell differentiation and activation. Here, we describe approaches for the in vitro assessment of NK cell metabolism. We present methods for using inhibitors to alter cellular metabolism, measurement of intracellular ATP in NK cells, assessment of real-time glycolysis and oxidative phosphorylation by an extracellular flux assay from Seahorse Biosciences, and some basic protocols for stimulation of NK cells via cytokines and receptors.