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The three principal reef types are:

1. Fringing reef – directly attached to a shore, or borders it with an intervening shallow channel or lagoon.
2. Barrier reef – reef separated from a mainland or island shore by a deep channel or lagoon.
3. Atoll reef – more or less circular or continuous barrier reef extends all the way around a lagoon without a central island.

Other reef types or variants are:

1. Patch reef – common, isolated, comparatively small reef outcrop, usually within a lagoon or embayment, often circular and surrounded by sand or sea grass.
2. Apron reef – short reef resembling a fringing reef, but more sloped; extending out and downward from a point or peninsular shore.
3. Bank reef – linear or semicircular shaped-outline, larger than a patch reef.
4. Ribbon reef – long, narrow, possibly winding reef, usually associated with an atoll lagoon.
5. Table reef – isolated reef, approaching an atoll type, but without a lagoon.
6. Habili – reef specific to the Red Sea; does not reach the surface near enough to cause visible surf; may be a hazard to ships.
7. Microatoll – community of species of corals; vertical growth limited by average tidal height; growth morphologies offer a low-resolution record of patterns of sea level change; fossilized remains can be dated using radioactive carbon dating and have been used to reconstruct Holocene sea levels.
8. Cays – small, low-elevation, sandy islands formed on the surface of coral reefs from eroded material that piles up, forming an area above sea level; can be stabilized by plants to become habitable; occur in tropical environments throughout the Pacific, Atlantic and Indian Oceans (including the Caribbean and on the Great Barrier Reef and Belize Barrier Reef), where they provide habitable and agricultural land.
9. Seamount or guyot – formed when a coral reef on a volcanic island subsides; tops of seamounts are rounded and guyots are flat; flat tops of guyots, or tablemounts, are due to erosion by waves, winds, and atmospheric processes