We report on the first global census of the Adélie Penguin (Pygoscelis adeliae), achieved using a combination of ground counts and satellite imagery, and find a breeding population 53% larger (3.79 million breeding pairs) than the last estimate in 1993. We provide the first abundance estimates for 41 previously unsurveyed colonies, which collectively contain 420,000 breeding pairs, and report on 17 previously unknown colonies. We think 11 of these previously unknown colonies may be recent colonizations. These recent colonizations represent approximately 5% of the increase in known breeding population and provide insight into the ability of these highly philopatric seabirds to colonize new breeding territories. Additionally, we report on thirteen colonies not found in the survey, including eight we conclude have gone extinct. Our global population assessment provides a robust baseline for understanding future changes in abundance and distribution, and finds that Adélie Penguin declines on the Antarctic Peninsula are more than offset by increases in East Antarctica. These results represent a critically-needed contribution to ongoing negotiations regarding the design and implementation of Marine Protected Areas for the Southern Ocean.