The changing face of the molecular evolutionary clock

•Genomic data have provided valuable insights into the molecular clock.•Genome sequences offer exciting prospects for estimating evolutionary timescales.•Placing a timescale on the Tree of Life relies on accurate models of rate variation. The molecular clock has played an important role in biological research, both as a description of the evolutionary process and as a tool for inferring evolutionary timescales. Genomic data have provided valuable insights into the molecular clock, allowing the patterns and causes of evolutionary rate variation to be characterized in increasing detail. I explain how genome sequences offer exciting opportunities for estimating the timescale of the Tree of Life. I describe the different approaches that have been used to deal with the computational and statistical challenges encountered in molecular clock analyses of genomic data. Finally, I offer a perspective on the future of molecular clocks, highlighting some of the key limitations and the most promising research directions.