This report summarizes the recent state of the California Current System (CCS), primarily during the period April 2005 through early 2006, and includes observations of ocean conditions made from Washington State south to Baja California. During 2005, the CCS experienced very unusual “ocean weather.” For example, off Washington, Oregon and northern California, the start of upwelling was delayed, resulting in anomalously warm sea surface temperatures through the spring and the early summer months. The warming observed in the northern California Current (NCC) in the spring and early summer appeared to be a regional phenomenon, since waters south of approximately 35 ̊N to the California–Mexico border were near the long-term average, and cooler-than-normal temperatures prevailed off Baja California. The extent of the warming and subsequent ecosystem response was similar to that of a major tropical El Niño event. However, we know from observations made at the equator that equatorial waters were in an El Niño-neutral state. The impacts on the NCC pelagic ecosystem were profound with very low biomass of zooplankton observed in Monterey Bay, the Gulf of the Farallones, and off Oregon, accompanied by unprecedented reproductive failure and mortality in several locally-breeding seabird species. Recruitment failure was seen in a variety of fishes as well. The proximate cause was a delay in the initiation of the upwelling season in the NCC (which usually begins in April) to a nearly unprecedented start time of late July. Thus, animals that reproduce in spring and in other years would find bountiful food resources, found themselves faced with famine rather than feast. Similarly, marine mammals and birds which migrate to the NCC upwelling region in spring and summer, which would otherwise find a high biomass of energetically-rich zooplankton and small pelagic fish upon which to feed, were equally disappointed. Moreover, 2005 marked the third year of chronically warm conditions in the NCC, a situation which could have led to a general reduction in physiological condition of fish and birds, rendering them less tolerant of adverse ocean conditions in 2005. INTRODUCTION This is the thirteenth in a series of annual reports prepared since 1993 that summarize the climatology, oceanography, and biology of the California Current System (CCS). It is the third to include data from the entire length of the California Current System. Programs or institutions contributing to this report include U.S.