Based on trace-fossil evidence, the Cambrian explosion emerges as one of the most dramatic events in the history of the biosphere. Ichnologic data are highly valuable as an independent line of evidence with respect to the body-fossil record and molecular clocks to explore the nature of this event and the associated evolutionary innovations. In contrast to body fossils, the trace-fossil record across the Ediacaran–Cambrian boundary is far more continuous, providing information on a critical time of ecosystem diversification and construction. The early Cambrian displayed a remarkable increase in both global and alpha ichnodiversity and ichnodisparity of bioturbation structures. Typical Cambrian architectural designs signal new ways of animal–sediment interactions recording the activities of a new cast of characters. This dramatic increase in ichnodiversity and ichnodisparity at the dawn of the Phanerozoic supports the Cambrian explosion scenario, and is hard to reconcile with the hypothesis that the sudden appearance of body fossils near the beginning of the Cambrian is simply a taphonomic artifact related to the acquisition of mineralized skeletons. The real nature of this event is further proved by comparing the microbial mat preservational window across the Ediacaran–Cambrian boundary. Distinct, sophisticated, undermat mining strategies diagnostic of Fortunian age are strikingly absent in Ediacaran rocks. In contrast to the body-fossil record that places the appearance of the main animal body plans by Cambrian Epoch 2, the trace-fossil record shows than the main diversification event took place by the Fortunian, allowing for a relatively short time (approximately 20 Ma) of phylogenetic fuse. The Fortunian diversification event expressed by the appearance of a wide variety of trace-fossil morphologies was decoupled from the major shift in benthic ecologic structure that took place later, during Cambrian Age 2 (i.e., Agronomic revolution). The Fortunian event marks the establishment of novel ways of interacting with the sediment resulting from the evolution of distinctive body plans and a wide repertoire of behavioral strategies. Sediment bulldozing in diffusion-dominated benthic systems, such as reworking of fine-grained offshore deposits, was characteristic of this phase of ecosystem engineering. The second (Cambrian Age 2) event in ecosystem engineering involves an evolutionary breakthrough in ecologic structuring. The ichnologic signature of this event is recorded by ichnofabrics dominated by vertical deep-tier suspension feeders (e.g., Skolithos piperock), revealing bioturbation in advection-dominated benthic systems. The establishment of suspension-feeding communities, in addition to the presence of a more complex tiering structure consisting of multiple ichnoguilds, suggests finely calibrated plankton to benthos exchange, recording an incipient Phanerozoic ecologic scenario already by Cambrian Age 2. Although the Cambrian explosion is commonly thought as restricted to shallow marine environments under normal-marine conditions (i.e., marine salinity and fully oxygenated), ichnologic information indicates that deep, oxygen-stressed- and marginal-marine environments, the latter including both shallow intertidal settings connected to the open sea and brackish-water embayed settings, were also involved in this evolutionary breakthrough. The presence of trace fossils in many classic Burgess Shale (BS) type deposits provides uncontroversial evidence of an in situ benthic community. In addition to oxygen (redox discontinuity surface very close to or at the sediment–water interface) as a controlling factor for the benthic community, early diagenetic processes and biomat development played a substantial role in the morphology and preservability of biogenic structures in BS-type deposits. Also, the absence of deep-tier colonization in early to middle Cambrian dysoxic settings and of a well-developed mixed layer opened a taphonomic window for the exceptional preservation of the small, delicate surficial and shallow-tier trace fossils so characteristic of these deposits. These conditions coexisted with intensely bioturbated deposits in more oxygenated, shallower-water deposits, pointing to the unusual environmental and taphonomic conditions of BS-type settings.