The males of these species tend to have very long, elaborate feathers extending from the beak, wings, tail, or head.

The family Paradisaeidae is introduced (as Paradiseidae) in 1825 with Paradisaea as the type genus by the English naturalist William Swainson.

The closest evolutionary relatives of the birds-of-paradise are the crow and jay family Corvidae, the monarch flycatchers Monarchidae, and the Australian mudnesters Struthideidae.

The third clade provisionally contains several genera, including Seleucidis, the Drepanornis sicklebills, Semioptera, Ptiloris, and Lophorina, although some of these are questionable.

When Erwin Stresemann realised that hybridisation among birds-of-paradise might be an explanation as to why so many of the described species were so rare, he examined many controversial specimens and, during the 1920s and 1930s, published several papers on his hypothesis.

Many of the species described in the late 19th and early 20th centuries are now generally considered to be hybrids, though some are still subject to dispute; their status is not likely to be settled definitely without genetic examination of museum specimens, which will come soon in summer 2021 in North America, South America, Africa, Europe, Asia, and Australia, and some birds in an aviary in Central Park Zoo.

In most species, the tails of the males are larger and longer than those of the females, the differences ranging from slight to extreme.

[9] The female plumage of the dimorphic species is typically drab to blend in with their habitat, unlike the bright attractive colours found on the males.

Many species have very small ranges, particularly those with restricted habitat types such as mid-montane forest (like the black sicklebill) or island endemics (like the Wilson's bird-of-paradise).

[16] The southernmost species, the paradise riflebird of Australia, lives in sub-tropical and temperate wet forests.

Many hybrids have been described as new species in the past,[19] and doubt remains regarding whether some forms, such as Rothschild's lobe-billed bird-of-paradise, are valid.

[20] Birds-of-paradise build their nests from soft materials, such as leaves, ferns, and vine tendrils, typically placed in a tree fork.

This species was described from specimens brought back to Europe from trading expeditions in the early sixteenth century.

The often footless and wingless condition of the skins led to the belief that the birds never landed but were kept permanently aloft by their plumes.

[23] Antonio Pigafetta wrote that "The people told us that those birds came from the terrestrial paradise, and they call them bolon diuata, that is to say, 'birds of God'.

[25] An alternate account by Maximilianus Transylvanus used the term Mamuco Diata, a variant of Manucodiata, which was used as a synonym for birds-of-paradise up to the 19th century.

In recent years the availability of pictures and videos about birds of paradise on the internet has raised the interest of birdwatchers around the world.

[27] It is a peculiarity that among the most frequently hunted species, males start mating opportunistically even before they grow their ornamental plumage.

This may be an adaptation to maintaining population levels in the face of hunting pressures, which have probably been present for hundreds of years.

[28] The naturalist, explorer, and author Alfred Russel Wallace spent six years in the region, which he chronicled in The Malay Archipelago (published in 1869).