The paradise flycatchers are generally small birds, around 18–21 cm (7.1–8.3 in) in length and weighing 12–23 g (0.42–0.81 oz). They have a medium length grey or blueish bill which is broad and hooked at the end and is surrounded by stiff rictal bristles. The inside of the mouths of paradise-flycatchers are brightly coloured, being either yellow or green. The tails are long, particularly in many species where the male has a massively elongated pair of middle tail feathers. These tail streamers are 195 mm long in the male Sao Tome Paradise-flycatcher and 412 mm long in the male Asian Paradise Flycatcher.
The function of the long tail is assumed to be related to sexual selection, with females choosing males based on the length of the tail.Not all species have long tail streamers, for example the Blue Paradise Flycatcher of Palawan in Asia and the Bedford's Paradise Flycatcher of montane Africa do not have exceptionally long tails. In most species the tail is longer than the wing, even in the shorter tailed females. The eye is surrounded by an eyering that is a blue thin wattle (slightly more pronounced in some species like the Rufous Paradise Flycatcher).
The plumage of the paradise flycatchers is sexually dimorphic, with rufous, white and black being the most common colours; one species has blue plumage and a few have traces of maroon. Sexual dimorphism can be pronounced (and of course more so in the long-tailed males) or subtle; the female Bedford's Paradise Flycatcher is identical to the male except slightly duller. Some species sport prominent crests. In some species, for example the Malagasy Paradise Flycatcher, the males have two or more colour morphs.