AMP-dependent protein kinase (AMPK) is an evolutionarily conserved serine/threonine protein kinase central to the regulation of energy balance at both the cellular and whole-body levels. In its classical role as an intracellular metabolic stress-sensing kinase, AMPK switches on fatty acid oxidation and glucose uptake in muscle, while switching off hepatic gluconeogenesis. AMPK also has a broader role in metabolism through the control of appetite. Regulation of AMPK activity at the whole-body level is coordinated by a growing number of hormones and cytokines secreted from adipose tissue, skeletal muscle, pancreas and the gut including leptin, adiponectin, insulin, interluekin-6, resistin, TNF-alpha and ghrelin. Understanding how these secreted signalling proteins regulate AMPK activity to control fatty acid oxidation, glucose uptake, gluconeogenesis and appetite may yield therapeutic treatments for metabolic disorders such as diabetes, insulin resistance and obesity.