TimeTree is a public knowledge-base for information on the tree-of-life and its evolutionary timescale. For those interested in published summaries of relationships and divergence times of major groups of organisms, see publications from Hedges and Kumar (2009) and Hedges et al. (2015). For reviews of the history and methods of time estimation, and other useful information, see RESOURCES. TimeTree is jointly directed by Blair Hedges and Sudhir Kumar (Temple University). We encourage suggestions for improvement of this resource (see CONTACT). Current staff members include: Glen Stecher, Bremen Braun, and Michael Suleski (Software and Database Developers), and Julie Marin, and Sarah Hanson (Data Research and Assembly). Previously we have been assisted by Brooke Gattens, Michael McCutchan, Kelly Boccia, Wayne Parkhurst, Tina Dennison, Mandy Hippenstiel, Audrie Kapinus, Lainey Lee, Jaclyn McKay, Molly Oberholtzer, Davide Pisani, Kathy Plavnik, Prachi Shaw, Lidsay Stork, Vinod Swarna, Graziela Valente, Curtis Williams, and Lin-Wei Wu. We continue to receive helpful feedback from our colleagues in the evolutionary biology community. This project has been supported, in part, by grants from the National Science Foundation, NASA Astrobiology Institute, and Science Foundation of Arizona.