The continental shelf, the region from the coastline to the edge of the continental slope, covers about eight percent of the global seafloor area. The continental shelf is a national asset for most nations. It is a source of fish, both commercial and sport, and in some areas it is also a source of oil and natural gas. Shelves are not of uniform width. They vary considerably in size off the coasts of the United States. They are almost negligible along Southern California's coast and Florida's southeast coast. Off Florida's west coast, however, the shelf extends 200 miles into the Gulf of Mexico. The average width worldwide is about forty miles.

Continental shelves look like the adjacent land. Coastal areas that are mountainous will have a continental shelf with similar features, which is the case off Southern California. Coastal areas dominated by low hills or plains are likely to have a shelf of nearly flat plains or low hills. This is observed along most of the US Atlantic and Gulf Coasts. Shelves off the mouths of larger rivers, such as the Mississippi, are usually broad with a large mud base of continental sediments.

Continental shelves along the coasts of the United States cover an area of about 891,000 square miles. Alaska's continental shelf alone occupies over 591,000 square miles. The Atlantic Coast's continental shelf covers 140,000 square miles, about equal to the land mass areas of New York, New Jersey, Ohio, and Pennsylvania combined. The Gulf of Mexico's continental shelf covers 135,000 square miles, nearly the same area as Nebraska and Iowa combined. The continental shelf off the coasts of California, Oregon, and Washington covers 25,000 square miles.