Interpretations of differing types of data, analyses, and modeling yield different rates of recurrence for Cascadia’s great (M8-9) megathrust earthquakes. Learning the source of these differences will improve seismic hazard assessments and forecasts. Understanding these differences will require asking fundamental questions about cycles of earthquake strain accumulation and release on various temporal and spatial scales, how earthquake ruptures nucleate and evolve, and how seismic energy is radiated. To address these questions the Cascadia Recurrence Project Team is undertaking an effort to produce a detailed and holistic knowledge of the history of Cascadia’s past megathrust events.  We are focusing on improving our understanding Cascadia earthquake history and processes by integrating the results of studies of earthquake-triggered 1) ground failures (particularly landslides), 2) coastal land-level changes, 3) tsunami inundation and deposition, and 4) offshore slope failures and turbidites.  Other contextual studies examine 5) structural controls on rupture segmentation, 6) rupture modeling, 7) seismic ground motion simulation and onshore and offshore site response, 8) modes of plate-boundary locking and slip, and 9) interactions among upper- and lower-plate faults.