The Northwest Nitrogen and Sulfur Critical Loads Workshop was co-sponsored by the Northwest Clean Air Agency, National Park Service (NPS), U.S. Department of Agriculture, Forest Service (USFS), and U.S. Geological Survey (USGS). Day 1 focused on presentations relating to management efforts and research related to nitrogen and sulfur critical loads. Day 2 (half day) focused on exploring research gaps and developing an agenda for future research activity to support setting nitrogen critical loads for northwest Class I areas, with a focus on Northwestern Washington. The Workshop was held at the North Cascades Environmental Learning Center September 6-7, 2006. Critical Load Concept A critical load is the quantitative estimate of an exposure of one or more pollutants below which significant harmful effects on specified sensitive elements of the environment do not occur according to present knowledge. The European Union and Canada have successfully used critical loads to manage air quality. Environment Canada is currently working on developing critical loads for sulfur and nitrogen for the Georgia Basin. There is growing interest in the U.S., especially from the Environmental Protection Agency (EPA) and the Federal Land Managers (FLMs) to establish and use critical loads. A critical load for eutrophication of high elevation aquatic ecosystems has been established for Rocky Mountain National Park (RMNP) at 1.5 kg N/ha/yr wet deposition.