Mammals have developed an endogenous circadian clock located in the suprachiasmatic nuclei (SCN) of the anterior hypothalamus that responds to the environmental light-dark cycle. Similar clocks are found in peripheral tissues, such as the liver and adipose tissue, regulating cellular and physiological functions. The circadian clock has been reported to regulate metabolism and energy homeostasis, including lipogenic and adipogenic pathways. This is achieved by mediating the expression and/or activity of certain metabolic enzymes and transport systems. In return, enzymes and transcription activators interact with and affect the core clock mechanism. Animals with clock gene mutations that disrupt cellular rhythmicity have provided evidence to the relationship between the circadian clock and metabolic homeostasis. In addition, clinical studies in obese patients accentuate the link between the circadian clock and metabolism. This review will focus on the inter-connection between the circadian clock and metabolism with implications for body weight and how the circadian clock is influenced by hormones that regulate metabolism.