The Stygian owl (Asio stygius) is a medium-sized "typical owl" in subfamily Striginae. It is found in Mexico, parts of Central America, Cuba, Hispaniola, and 10 countries in South America.

The Stygian owl has these six recognized subspecies:

The Stygian owl is 38 to 46 cm (15 to 18 in) long and weighs about 400 to 675 g (14 to 24 oz). The sexes have similar very dark plumage. (The adjective "Stygian" means "of, or relating to, the River Styx", but is more widely applied to anything that is dark or dismal.) The face is blackish with a pale border and a whitish forehead, and the head has long dark feathers that project upward as "ears". The dark upperparts have buff streaks and bars; the underparts are a dingy buff with dark brown or blackish barring and streaks. The eye is shades of yellow, the bill blue-black to blackish, and the feet dark grayish or brownish pink. Its eyes may appear to be a shade of crimson under certain lighting due to their reflective nature. The subspecies are substantially alike, differing mostly in the shade of the upperparts' streaks and somewhat in size.

The subspecies of Stygian owl are found thus (but see the text below the list):

In addition, the Stygian owl has been documented as a vagrant in Texas, Florida, and Trinidad.

Some authors merge A. s. lambi into A. s. robustus. Some extend the range of robustus to include the Colombian, Ecuadorian, and Venezuelan populations otherwise attributed to A. s. stygius. Some include A. s. noctipetens in A. s. siguapa. And some include the population in southeastern Brazil in A. s. barberoi instead of in A. s. stygius.

The Stygian owl inhabits a wide variety of landscapes from sea level to 3,000 m (9,800 ft) of elevation. Most are fairly open rather than densely forested or purely grasslands. They include montane pine, pine-oak, and cloud forests, thorn scrub, cerrado, pine plantations, and even urban parks.

As far as is known, the Stygian owl is resident throughout its range.