Over the past one hundred years, dramatic changes have taken place in populations of colonial-nesting seabirds that breed within Chesapeake Bay and the Maryland-Virginia coastal region. Populations of species that were decimated by extensive market hunting in the late nineteenth century recovered, additional species colonized the region and in the past ten years many species have declined. During 2003, over 72,000 pairs of seabirds of thirteen species bred within the region. Breeding population sizes are presented and population trends evaluated based on benchmark census information from 1977 and regional censuses compiled during 1993 and 2003 by the states of Maryland and Virginia. Since the 1970s, Brown Pelicans (Pelicanus occidentalis) and Double-crested Cormorants (Phalacrocorax auritus) expanded into the region and now represent six percent of the seabird guild. Gull populations have exhibited important changes and have affected other seabird species. Significant population declines have occurred in Black Skimmers (Rynchops niger), Gull-billed Terns (Sterna nilotica), Royal Terns (Sterna maxima), and Common Terns (Sterna hirundo). Since 1993, populations of ten of thirteen seabird species have declined, many significantly. Conservation challenges for seabird species in the region include: 1) habitat change and loss as a result of sea-level rise, 2) increasing mammalian predator populations, 3) competition for colony sites, 4) human infrastructure conflicts, and 5) changing fisheries populations and harvest. Conserving and managing colonial-nesting seabirds in the coming decades as the human population continues to increase in the mid-Atlantic region will present significant challenges to future generations.