Life is a continual battle to stay in a non-equilibrium energy state. Living things must obtain energy from the environment and effectively use it to drive metabolic reactions. ‘Circadian rhythms and metabolism’ shows that the circadian timing of energy metabolism, of which blood glucose levels are a major part, is a multi-layered system involving control by the suprachiasmatic nucleus, as well as by peripheral clocks in organs such as the liver, pancreas, muscle, and white adipose tissue. Several hormones also play an important role. The complex interactions between the suprachiasmatic nucleus, hypothalamus, hormones, and other signalling molecules involved in the circadian regulation of metabolism is mirrored at the subcellular level.