We are interested in understanding the genetic and molecular basis of circadian rhythms as well as other complex behaviors. We use forward genetic approaches in the mouse to discover genes regulating the nervous system and behavior. The circadian clock in animals involves an autoregulatory transcriptional feedback loop in which CLOCK and BMAL1 activate the transcription of the Period and Cryptochrome genes. The PERIOD and CRYPTOCHROME proteins then feedback and repress their own transcription by interaction with CLOCK and BMAL1. We have studied the biochemistry of the CLOCK:BMAL1 transcriptional activator complex as well as the genomic targets of CLOCK and BMAL1 using ChIP-seq methods. CLOCK and BMAL1 interact with the regulatory regions of thousands of genes. The gene network and dynamics of the system will be discussed. More recently we have also used forward genetic approaches to understand other behaviors such as the response to psychostimulants as well as learning and memory.