This assessment report presents the results of the 2013 AMAP Assessment of Arctic Ocean Acidification (AOA). This is the first such assessment dealing with AOA from an Arctic-wide perspective, and complements several assessments that AMAP has delivered over the past ten years concerning the effects of climate change on Arctic ecosystems and people. This report provides the accessible scientific basis and validation for the statements and recommendations made in the Arctic Ocean Acidification Assessment Summary for Policy-makers1 that was delivered to Arctic Council Ministers at their meeting in Kiruna, Sweden in May 2011 and the related AMAP State of the Arctic Environment report Arctic Ocean Acidification 2013: An Overview2. It includes extensive background data and references to the scientific literature, and details the sources for figures reproduced in the overview report.