The aerosol over the world oceans plays an important role in determining the physical and chemical characteristics of the Earth's atmosphere and its interactions with the climate system. The oceans contribute to the aerosols in the overlying atmosphere by the production and emission of aerosol particles and precursor gases. The marine aerosol, in turn, influences the biogeochemistry of the surface ocean through long distance transport and deposition of terrestrial and marine-derived nutrients and other chemicals. This chapter is an introduction to the physical and chemical properties of marine aerosols, to processes determining their composition and behavior, and to some of the issues driving current research in this field. Copyright 2009 by the American Geophysical Union.