Autophagy is an essential factor for intracellular metabolism and the maintenance of cellular homeostasis. Certain tumor cells have a higher basal autophagy rate, and inhibiting autophagy can impair metabolic function in autophagy-dependent tumor cells. The autophagy status in immune cells determines their fate and response to antigen; however, autophagy in immune cells can be beneficial or detrimental depending on the cell’s developmental stage and, more specifically, its degree of differentiation. Variations in many metabolites, proteins, and enzymes in autophagy-deficient hosts may have tumor-promoting or tumor-inhibiting effects. The importance of autophagy in the metabolism of some cancers and immune cells makes it a critical target whose mechanisms must be better understood in order to optimize patient response and prevent tumor recurrence.