El Niño events were first perceived several centuries ago as a dramatic change in the marine resources along the Peruvian coast. It is now recognized as part of the world’s largest natural climate fluctuation: the El Niño Southern Oscillation (ENSO). There is a rapidly growing body of scientific literature showing that ENSO has physical and ecological impacts throughout the Pacific Ocean and more broadly across the other oceanic basins through atmospheric teleconnections. This review details a range of these examples in all major ecosystems impacted by ENSO in the Pacific Ocean. Teleconnections with other basins are also discussed, as are the diversity of changes associated with ENSO phases and their consequences on fisheries sustained by these ecosystems. Information is provided on the emerging complexity of the connection between ENSO and the ocean ecosys-tems, and particularly the diversity of El Niño types, characterized by eastern and central spatial patterns and differences in intensity. As these mechanisms become better understood, useful predictive capacity for ecosystem and fisheries management will result. However, growing evidences suggest that climate change may have already started interacting with ENSO dynamics and effects, complicating mechanistic understanding.