Mokosh (/ˈmɒkɒʃ/ ^ⓘ MOK-osh) is a Slavic goddess. No narratives about this deity have survived and scholars must rely on academic disciplines like philology to discern details about her.

According to etymological reconstruction, Mokosh was the goddess of earth, waters and fertility. Later, according to most researchers, she was reflected in bylinas and zagovory as Mat Zemlya, the personification of Earth in East Slavic folklore. Another reconstruction was made on the basis of ethnography; at the end of the 19th century, the names kikimora as Mokusha or Mokosha were recorded in the Russian North. The coincidence is explained by kikimora being a demonized version of the goddess and, by approximating between the two, researchers have portrayed Mokosh as the goddess of love and birth, with a connection to night, the moon, spinning, sheep farming and women's economy. Spinning was the occupation of several European goddesses of fate, which led to the characterization of Mokosh as a deity who controls fate. This reconstruction disagrees with data on her etymology, which shows spinning could not have been the deity's main role.

In 980, prince Vladimir the Great established a wooden statue of Mokosh, along with other deities, on a hill in Kyiv, Ukraine. Some historians have described this event as a manifestation of Vladimir's pagan reformation but other scholars deny such a reformation was carried out, and the question of its existence is debatable in modern scholarship. In 998, during the Christianization of Kievan Rus', statues of deities were destroyed. Mokosh was mentioned in various Words and Teachings against Paganism along with the vilas, but is not described by them.

In academia, the opinion has spread that the cult of Mokosh has passed to the folk-Christian Paraskeva Friday, the personification of Friday associated with water and spinning. Because of this identification, Paraskeva began to be considered a day dedicated to the goddess, and a conclusion about the popularity of Mokosh among women in Christian times was drawn. In later studies, the idea of an approximation with Paraskeva was criticized because Paraskeva's association with spinning, water, and Friday has Christian rather than pagan roots.

The Slavic version of the basic myth theory, based on ethnographic and linguistic data, depicts Mokosh as Perun's wife. It is believed Mokosh cheated on Perun with Veles, causing Perun to kill Mokosh's children. The theory has not been recognized in academia. The supposition Mokosh is depicted on the Zbruch Idol and on North Russian 19th-century embroideries has also been rejected. Archaeologist Boris Rybakov's theory the goddess' original name was Makosh is not supported by other researchers.

In Old East Slavic texts, the name Mokosh is rendered as Mokošĭ (мокошь), Mokŭšĭ (мокъшь) – in ancient texts uppercase was not used. According to Oleg Trubachyov, the form Mokŭšĭ was formed through the secondary adideation of *Mokošь and *kъšь "fate". Grammatically, the theonym Mokosh belongs to the feminine gender, from which it is inferred that the deity was specifically a goddess. In older studies and later chronicles, she may have appeared to be a male deity, but this variant is secondary to the original. According to the most-reasonable and widespread etymology the theonym was formed by the suffixal method from the Proto-Slavic stem *mok- meaning "wet" with the suffix *-ošь. Vladimir Toporov and Vyacheslav Ivanov comment this etymology is "indisputable", understanding her name as "She who is wet". The first to put forward such an etymology was Vatroslav Jagić, who believed the theonym is a translation or an amplification of the Greek word malakiya, and therefore Mokosh was a literary fiction. Toporov, Ivanov and Max Vasmer consider Jagić's position to be incorrect.

According to Michał Łuczyński, the theonym may have appeared after the 3rd century AD due to the occurrence of the [š] sound, which arose in Slavic languages as part of the first palatalization. He derives the name of the goddess from the unattested noun *mokošь "someone/something wet" because the suffix *-ošь forms the names of the bearers of features, and he drives this noun from the v-tematic *moky (gen *mokъve) "wet place, mud" (cf. Polish dial. mokwa, Ukrainian mokva) and compares the name Mokosh to other names ending in -osh that are derived from v-thematic words with topographical meaning, e.g. Old Polish Bagosz (< *bagy), Narosz (< *nary). In connection with this etymology, he considers Mokosh to be a "pluvial goddess with uranic characteristics". Similarly, Valeriy Mokiyenko [Wikidata] understands the theonym to derive from a word meaning "moist, swampy place". Toporov, Ivanov, and Łuczyński believe the theonym Mokosh is a later epithet that replaced the original, unknown name of the deity. Ivanov and Toporov compare the etymology with Lithuanian makusyti "to splash", "to walk on mud"; makasyne "slush", "mud", "mixture", "mess".

Vasmer and many modern academics consider Mokosh to be the goddess of fertility, waters and earth, which brings her closer to the later Mat Zemlya, who is often mentioned in bylinas and zagovory. Aleksander Gieysztor commented that the association with Mat Zemlya is shared by most researchers. Mokiyenko and Henryk Łowmiański also suggested a connection with rain.