Transcription is the first step necessary to utilize genetic information. The activation or repression of genes is highly regulated. Here, we will shed light on the connection between transcription and the circadian oscillator. Circadian oscillators are based on interconnected transcriptional and post-translational feedback loops. In this manner, they are capable to establish and maintain robust free-running rhythms with a period length of about a day. To adjust the phase, it is enough to manipulate the accumulation of some oscillator components. Since the oscillator generates robust rhythms, this simple variation is sufficient to shift the phase of the circadian oscillator for the next day. To govern rhythmic output processes, target genes are either hardwired to the oscillator, or regulated by rhythmic transcriptional regulators as intermediaries. This generates complex, tissue-specific circadian networks of gene expression.