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The recent discovery of episodic tremor and slip (ETS) in subduction zones is based on slow slip episodes visible in global positioning system observations correlated with nonvolcanic tremor signals on seismometers. ETS occurs just inboard from a region capable of great megathrust earthquakes; however, whether there is any communication between these two processes remains unknown. In this study we use new single-station methods to compile an ETS catalog for the entire Cascadia subduction zone, offshore western North America, and compare the patterns with a variety of along-strike trends for the subducting and overriding plates. Correlated ground vibrations and strain observations are found all along the subduction zone, demonstrating that ETS is an inherent part of the subduction process. There are three broad (300–500 km), coherent zones with different recurrence intervals (14 ± 2, 19 ± 4, 10 ± …