The Chukchi Offshore Monitoring in Drilling Area (COMIDA) aerial survey component was initiated in 2008, via an Interagency Agreement (No. M08PG20023) between the Minerals Management Service (MMS) [Department of the Interior; currently the Bureau of Ocean Energy Management, Regulation and Enforcement] and the National Marine Mammal Laboratory (NMML) [Alaska Fisheries Science Center, National Marine Fisheries Service, National Oceanic and Atmospheric Administration, Department of Commerce]. These surveys are a continuation of aerial surveys that were conducted by MMS-sponsored contractors from 1982-1991 (Ljungblad et al., 1987; Moore and Clarke, 1992) and use similar methodology. Aerial surveys remain the only practical means of assessing marine mammal distribution, population density, and habitat use in large study areas. The goal of this study is to investigate the distribution and relative abundance of marine mammals in the Chukchi Sea Planning Area (CSPA) during the open water (ice-free) months of June-October, when various species are undertaking seasonal migrations through the area. The COMIDA study area encompasses the northeastern Chukchi Sea from shore seaward, latitude 68°N to 72°N and longitude 157°W to 169°W, and overlays Lease Sale 193 (offered in February 2008). Species of interest include the bowhead whale (Balaena mysticetus), gray whale (Eschrichtius robustus), beluga (Delphinapterus leucas), polar bear (Ursus maritimus), walrus (Odobenus rosmarus), and ice seals. Increasing the understanding of marine mammal distribution, abundance and migration timing in this region will assist in decision-making to minimize impacts from petroleum exploration, development and production activities and other anthropogenic impacts.