The AMP-activated protein kinase (AMPK) is a key metabolic regulator that both senses changes in cellular energy levels and activates pathways to maintain cellular energy balance. AMPK achieves this by stimulating catabolic pathways that generate ATP and inhibiting biological pathways that consume ATP consumption. Recent work has established that AMPK is activated in T cells by both immunological and environmental stimuli, and plays an important role in T cell metabolism, in part by controlling T cell ‘metabolic plasticity’. Recent data have revealed distinct functions for AMPK in T cells, including effects on memory T cell development, cytokine production, and potentially anti-tumor responses. In this review, we discuss recent advances in our understanding of AMPK function in T cells, and discuss future research areas for this energy-sensing pathway in lymphocytes.