Lemurs (pron-en?li?m?r, USdictl??�m?r) are a clade of strepsirrhine (strepsirrhini) primates endemic (endemism) to the island of Madagascar. They are named after the lemures (ghosts or spirits) of Roman mythology due to the ghostly vocalizations, reflective eyes, and the nocturnal (nocturnal animal) habits of some species. Although lemurs often are confused with ancestral primates, the anthropoid (Simian) primates (monkeys, apes, and humans) did not evolve from them; instead, lemurs merely share morphological and behavioral traits with basal (basal (phylogenetics)) primates. Lemurs arrived in Madagascar around 62 to 65 mya (Year#Symbols y and yr) by rafting (rafting event) on mats of vegetation at a time when ocean currents favored oceanic dispersal to the island. Since that time, lemurs have evolved (Evolution) to cope with an extremely seasonal environment and their adaptations give them a level of diversity that rivals that of all other primate groups. Until shortly after humans arrived on the island around 2,000 years ago, there were lemurs as large as a male gorilla. Today, there are nearly 100 species of lemurs (List of lemur species), and most of those species were discovered or promoted to full species status since the 1990s; however, lemur taxonomic classification (taxonomy) is controversial and depends on which species concept is used. Even the higher-level taxonomy is disputed, with some experts preferring to place most lemurs within the infraorder (Taxonomic rank) Lemuriformes, while others prefer Lemuriformes to contain all living strepsirrhines, placing all lemurs in superfamily (Taxonomic rank) Lemuroidea and all lorises and galagos in superfamily Lorisoidea.

Ranging in size from 30 g (1.1 oz) to 9 kg (20 lb), lemurs share many common, basal primate traits, such as divergent digits (digit (anatomy)) on their hands and feet and nails (nail (anatomy)) instead of claws (in most species). However, their brain-to-body size ratio (Brain-to-body mass ratio) is smaller than that of anthropoid primates, and among many other traits they share with other strepsirrhine primates, they have a "wet nose" (rhinarium). Lemurs are generally the most social of the strepsirrhine primates and communicate more with scents and vocalizations than with visual signals. Many lemur adaptations are in response to Madagascars highly seasonal environment. Lemurs have relatively low basal metabolic rates and may exhibit seasonal breeding (seasonal breeder), dormancy (such as hibernation or torpor), or female social dominance (dominance (ethology)). Most eat a wide variety of fruits and leaves, while some are specialists. Although many share similar diets, different species of lemur share the same forests by differentiating niches (niche differentiation).

Lemur research focused on taxonomy and specimen collection during the 18th and 19th centuries. Although field observations trickled in from early explorers, modern studies of lemur ecology and behavior did not begin in earnest until the 1950s and 1960s. Initially hindered by political instability and turmoil on Madagascar during the mid-1970s, field studies resumed in the 1980s and have greatly increased our understanding of these primates. Research facilities like the Duke Lemur Center have provided research opportunities under more controlled settings. Lemurs are important for research because their mix of primitive characteristics and traits shared with anthropoid primates can yield insights on primate and human evolution. However, many lemur species are threatened with extinction due to habitat loss and hunting. Although local traditions generally help protect lemurs and their forests, illegal logging (Illegal logging in Madagascar), widespread poverty, and political instability hinder and undermine conservation efforts.