Seilacher's publications are numerous (well over 200) and cover a range of topics. His studies on trace fossils are perhaps his best-known contributions, especially his 1967 work on the bathymetry of trace fossils. Here he established the concept of ichnofacies: distinctive assemblages of trace fossils controlled largely by depth. This characterisation was later expanded to include the influences of substrate, oxygen, salinity and so on. In addition, he analysed many trace fossils in terms of the behaviour they represent, leading to such work as early computer simulation of trace fossil morphology (with David Raup, in 1969). Much of this work is summarized together with new material in "Trace Fossil Analysis" (2007).