Gracias a la colaboración de numerosos biólogos, este sitio, que contiene más de 4.000 páginas, proporciona información sobre la diversidad de los organismos, su historia evolutiva y otras características:
«Each page contains information about a particular group of organisms (e.g., echinoderms, tyrannosaurs, phlox flowers, cephalopods, club fungi, or the salamanderfish of Western Australia). ToL pages are linked one to another hierarchically, in the form of the evolutionary tree of life. Starting with the root of all Life on Earth and moving out along diverging branches to individual species, the structure of the ToL project thus illustrates the genetic connections between all living things.»