Strepsirrhini or Strepsirhini (/ˌstrɛpsəˈraɪni/ ^ⓘ; STREP-sə-RY-nee) is a suborder of primates that includes the lemuriform primates, which consist of the lemurs of Madagascar, galagos ("bushbabies") and pottos from Africa, and the lorises from India and Southeast Asia. Collectively they are referred to as strepsirrhines.

Also belonging to the suborder are the extinct adapiform primates, which thrived during the Eocene in Europe, North America, and Asia, but disappeared from most of the Northern Hemisphere as the climate cooled. Adapiforms are sometimes referred to as being "lemur-like", although the diversity of both lemurs and adapiforms does not support this comparison.

Strepsirrhines are defined by their "wet" (moist) rhinarium (the tip of the snout) – hence the colloquial but inaccurate term "wet-nosed" – similar to the rhinaria of canines and felines. They also have a smaller brain than comparably sized simians, large olfactory lobes for smell, a vomeronasal organ to detect pheromones, and a bicornuate uterus with an epitheliochorial placenta. Their eyes contain a reflective layer to improve their night vision, and their eye sockets include a ring of bone around the eye, but they lack a wall of thin bone behind it.

Strepsirrhine primates produce their own vitamin C, whereas haplorhine primates must obtain it from their diets. Lemuriform primates are characterized by a toothcomb, a specialized set of teeth in the front, lower part of the mouth mostly used for combing fur during grooming.

Many of today's living strepsirrhines are endangered due to habitat destruction, hunting for bushmeat, and live capture for the exotic pet trade. Both living and extinct strepsirrhines are behaviorally diverse, although all are primarily arboreal (tree-dwelling). Most living lemuriforms are nocturnal, while most adapiforms were diurnal. Both living and extinct groups primarily fed on fruit, leaves, and insects.

The taxonomic name Strepsirrhini derives from the Greek στρέψις strepsis "a turning round" and ῥίς rhis "nose, snout, (in pl.) nostrils" (GEN ῥινός rhinos), which refers to the appearance of the sinuous (comma-shaped) nostrils on the rhinarium or wet nose. The name was first used by French naturalist Étienne Geoffroy Saint-Hilaire in 1812 as a subordinal rank comparable to Platyrrhini (New World monkeys) and Catarrhini (Old World monkeys). In his description, he mentioned "Les narines terminales et sinueuses" ("Nostrils terminal and winding").

When British zoologist Reginald Innes Pocock revived Strepsirrhini and defined Haplorhini in 1918, he omitted the second "r" from both ("Strepsirhini" and "Haplorhini" instead of "Strepsirrhini" and "Haplorrhini"), although he did not remove the second "r" from Platyrrhini or Catarrhini, both of which were also named by É. Geoffroy in 1812. Following Pocock, many researchers continued to spell Strepsirrhini with a single "r" until primatologists Paulina Jenkins and Prue Napier pointed out the error in 1987.

Strepsirrhines include the extinct adapiforms and the lemuriform primates, which include lemurs and lorisoids (lorises, pottos, and galagos). Strepsirrhines diverged from the haplorhine primates near the beginning of the primate radiation between 55 and 90 mya. Older divergence dates are based on genetic analysis estimates, while younger dates are based on the scarce fossil record. Lemuriform primates may have evolved from either cercamoniines or sivaladapids, both of which were adapiforms that may have originated in Asia. They were once thought to have evolved from adapids, a more specialized and younger branch of adapiform primarily from Europe.