Circadian metabolic rhythms are fundamental to the control of nutrient and energy homeostasis, as well as the pathogenesis of metabolic disease, such as obesity, lipid disorders, and type 2 diabetes. This temporal organization of tissue metabolism is coordinated through reciprocal cross talk between the biological timing system and the metabolic regulatory networks. In this review, we discuss the signaling mechanisms that serve to couple metabolic regulation to the circadian pacemaker, in particular the role of the peroxisome proliferator-activated receptor-γ coactivator-1 transcriptional coactivators in integrating clock and energy metabolism.