Seabirds are birds that are adapted to life within the marine environment. While seabirds vary greatly in lifestyle, behaviour and physiology, they often exhibit striking convergent evolution, as the same environmental problems and feeding niches have resulted in similar adaptations. The first seabirds evolved in the Cretaceous period, and modern seabird families emerged in the Paleogene,

Albatrosses are very large seabirds in the family Diomedeidae. They range widely in the Southern Ocean and the North Pacific. They are absent from the North Atlantic, although fossil remains show they once occurred there and occasional vagrants are found. Albatrosses are among the largest of flying birds, and species of the genus Diomedea have the longest wingspans of any extant birds, reaching up to 3.7 m. Albatrosses are usually regarded as falling into four genera, but disagreement exists over the number of species.

Austral storm petrels, or southern storm petrels, are seabirds in the family Oceanitidae, part of the order Procellariiformes. These smallest of seabirds feed on planktonic crustaceans and small fish picked from the surface, typically while hovering. Their flight is fluttering and sometimes bat-like.

Charadriiformes is a diverse order of small to medium-large birds. It includes about 350 species and has members in all parts of the world. Most charadriiform birds live near water and eat invertebrates or other small animals; however, some are pelagic (seabirds), others frequent deserts, and a few are found in dense forest.

Phalacrocoracidae is a family of approximately 40 species of aquatic birds commonly known as cormorants and shags. Several different classifications of the family have been proposed recently and the number of genera is disputed. The great cormorant and the common shag are the only two species of the family commonly encountered on the British Isles and "cormorant" and "shag" appellations have been later assigned to different species in the family somewhat haphazardly.

Frigatebirds are a family of seabirds called Fregatidae which are found across all tropical and subtropical oceans. The five extant species are classified in a single genus, Fregata. All have predominantly black plumage, long, deeply forked tails and long hooked bills. Females have white underbellies and males have a distinctive red gular pouch, which they inflate during the breeding season to attract females. Their wings are long and pointed and can span up to 2.3 metres (7.5 ft), the largest wing area to body weight ratio of any bird.

The fulmars are tubenosed seabirds of the family Procellariidae. The family consists of two extant species and two extinct fossil species from the Miocene.

The fulmarine petrels or fulmar-petrels are a distinct group of petrels within the family Procellariidae. They are the most variable of the four groups within the Procellariidae, differing greatly in size and biology. They do, however, have a unifying feature, their skull, and in particular their nasal tubes. They are predominantly found in the Southern Ocean with one species, the northern fulmar, ranging in the North Pacific and Atlantic Oceans.

Gannets are seabirds comprising the genus Morus, in the family Sulidae, closely related to boobies. "Gannet" is derived from Old English ganot, ultimately from the same Old Germanic root as "gander". Morus is derived from Ancient Greek moros, "foolish", due to the lack of fear shown by breeding gannets and boobies, allowing them to be easily killed.

Gulls, or colloquially seagulls, are seabirds of the family Laridae in the suborder Lari. They are most closely related to the terns and only distantly related to auks, skimmers and even more distantly to waders. Until the 21st century, most gulls were placed in the genus Larus, but that arrangement is now considered polyphyletic, leading to the resurrection of several genera. An older name for gulls is mews, which is cognate with German Möwe, Danish måge, Swedish mås, Dutch meeuw, and French mouette, and can still be found in certain regional dialects.

Seabirds include some of the most threatened taxa anywhere in the world. For example, of extant albatross species, 82% are listed as threatened, endangered, or critically endangered by the International Union for Conservation of Nature. The two leading threats to seabirds are accidental bycatch by commercial fishing operations and introduced mammals on their breeding islands. Mammals are typically brought to remote islands by humans either accidentally as stowaways on ships, or deliberately for hunting, ranching, or biological control of previously introduced species. Introduced mammals have a multitude of negative effects on seabirds including direct and indirect effects. Direct effects include predation and disruption of breeding activities, and indirect effects include habitat transformation due to overgrazing and major shifts in nutrient cycling due to a halting of nutrient subsidies from seabird excrement. There are other invasive species on islands that wreak havoc on native bird populations, but mammals are by far the most commonly introduced species to islands and the most detrimental to breeding seabirds. Despite efforts to remove introduced mammals from these remote islands, invasive mammals are still present on roughly 80% of islands worldwide.

Laridae is a family of seabirds in the order Charadriiformes that includes the gulls, terns and skimmers. It includes around 100 species arranged into 22 genera. They are an adaptable group of mostly aerial birds found worldwide.

Muttonbirding is the seasonal harvesting of the chicks of petrels, especially shearwater species, for food, oil and feathers by recreational or commercial hunters. Such hunting of petrels and other seabirds has occurred in various locations since prehistoric times, and there is evidence that many island populations have become extinct as a result. More recently ‘muttonbirding’ usually refers to the regulated and sustainable harvesting of shearwaters in Australia and New Zealand. These include the short-tailed shearwater, also known as the yolla or Australian muttonbird, in Bass Strait, Tasmania, as well as the sooty shearwater, also known as the titi or New Zealand muttonbird, on several small islands known as the Muttonbird Islands, scattered around Stewart Island in the far south of New Zealand.

The Pelecaniformes are an order of medium-sized and large waterbirds found worldwide. As traditionally—but erroneously—defined, they encompass all birds that have feet with all four toes webbed. Hence, they were formerly also known by such names as totipalmates or steganopodes. Most have a bare throat patch, and the nostrils have evolved into dysfunctional slits, forcing them to breathe through their mouths. They also have a pectinate nail on their longest toe. This is shaped like a comb and is used to brush out and separate their feathers. They feed on fish, squid, or similar marine life. Nesting is colonial, but individual birds are monogamous. The young are altricial, hatching from the egg helpless and naked in most. They lack a brood patch.

Penguins are a group of aquatic flightless birds. They live almost exclusively in the Southern Hemisphere, with only one species, the Galápagos penguin, found north of the equator. Highly adapted for life in the water, penguins have countershaded dark and white plumage and flippers for swimming. Most penguins feed on krill, fish, squid and other forms of sea life which they catch while swimming underwater. They spend roughly half of their lives on land and the other half in the sea.

Petrels are tube-nosed seabirds in the bird order Procellariiformes.

The Phaethontiformes are an order of birds. They contain one extant family, the tropicbirds (Phaethontidae), and one extinct family Prophaethontidae from the early Cenozoic. Several fossil genera have been described.

The family Procellariidae is a group of seabirds that comprises the fulmarine petrels, the gadfly petrels, the prions, and the shearwaters. This family is part of the bird order Procellariiformes, which also includes the albatrosses, the storm petrels, and the diving petrels.

Procellariiformes is an order of seabirds that comprises four families: the albatrosses, petrels and shearwaters, and 2 families of storm petrels. Formerly called Tubinares and still called tubenoses in English, procellariiforms are often referred to collectively as the petrels, a term that has been applied to all members of the order, or more commonly all the families except the albatrosses. They are almost exclusively pelagic, and have a cosmopolitan distribution across the world's oceans, with the highest diversity being around New Zealand.

The Southern African Foundation for the Conservation of Coastal Birds (SANCCOB) is an international body dedicated to seabird rehabilitation. The only seabird rehabilitation organisation registered with the South African Veterinary Council, the non-profit centre is based at the Rietvlei Wetland Reserve in Table View, South Africa.

The term seabird is used for many families of birds in several orders that spend the majority of their lives at sea. Seabirds make up some, if not all, of the families in the following orders: Procellariiformes, Sphenisciformes, Pelecaniformes, and Charadriiformes. Many seabirds remain at sea for several consecutive years at a time, without ever seeing land. Breeding is the central purpose for seabirds to visit land. The breeding period is usually extremely protracted in many seabirds and may last over a year in some of the larger albatrosses; this is in stark contrast with passerine birds. Seabirds nest in single or mixed-species colonies of varying densities, mainly on offshore islands devoid of terrestrial predators. However, seabirds exhibit many unusual breeding behaviors during all stages of the reproductive cycle that are not extensively reported outside of the primary scientific literature.

Seawatching is a type of birdwatching where participants observe seabirds from a fixed point on the mainland. They may do this from a coastal location, usually a headland, looking out to sea, or from a boat or ship.

Shearwaters are medium-sized long-winged seabirds in the petrel family. They have a global marine distribution, but are most common in temperate and cold waters, and are pelagic outside the breeding season.

The skuas are a group of predatory seabirds with seven species forming the genus Stercorarius, the only genus in the family Stercorariidae. The three smaller skuas are called jaegers in American English.

Northern storm petrels are seabirds in the family Hydrobatidae, part of the order Procellariiformes. The family was once lumped with the similar austral storm petrels in the combined storm petrels, but have been split, as they were not closely related. These smallest of seabirds feed on planktonic crustaceans and small fish picked from the surface, typically while hovering. Their flight is fluttering and sometimes bat-like.

The order Suliformes is an order recognised by the International Ornithologist's Union. In regard to the recent evidence that the traditional Pelecaniformes is polyphyletic, it has been suggested that the group be split up to reflect the true evolutionary relationships.

Tropicbirds are a family, Phaethontidae, of tropical pelagic seabirds. They are the sole living representatives of the order Phaethontiformes. For many years they were considered part of the Pelecaniformes, but genetics indicates they are most closely related to the Eurypygiformes. There are three species in one genus, Phaethon. The scientific names are derived from Ancient Greek phaethon, "sun". They have predominantly white plumage with elongated tail feathers and small feeble legs and feet.