Ichnology involves the study of traces produced by organisms (both animals and plants) on or within a substrate, and includes all issues related to bioturbation, bioerosion, and biodeposition (Pemberton et al., 1992a; Bromley, 1990, 1996). As such, ichnology encompasses both the study of processes, and their resulting products. The processes are all those involved in the interaction between organisms and substrates. The products are the traces themselves, which comprise individual and distinctive structures of biogenic origin, particularly those related more or less directly to the morphologies of the producers (Frey, 1973), and any sedimentary fabric resulting from biogenic reworking of the substrate, including non-discrete mottlings (i.e. biodeformational structures). Ichnology comprises two main fields: neoichnology (the study of modern traces or lebensspuren of classic German papers) and paleoichnology (the study of their fossil counterparts: trace fossils or ichnofossils). In this chapter, we review the conceptual framework of ichnology. We start by introducing basic concepts and outlining the 10 most important characteristics of trace fossils. Then we discuss aspects of trace-fossil preservation, including different schemes to classify biogenic structures in this respect. Finally, we turn our attention to the potential of trace fossils as sources of behavioral information, providing an in-depth discussion of the ethological classification.