Louisiana Voodoo, also known as New Orleans Voodoo, was an African diasporic religion that existed in Louisiana and the broader Mississippi River valley between the 18th and early 20th centuries. It arose through a process of syncretism between the traditional religions of West and Central Africa, Haitian Vodou, and Catholicism. No central authority controlled Louisiana Voodoo, which was organized through autonomous groups.

From the early 18th century, enslaved West and Central Africans—the majority of them Bambara and Bakongo—were brought to the French colony of Louisiana. There, their traditional religions syncretized with each other and with the Catholic beliefs of the French. This continued as Louisiana came under Spanish control and was then purchased by the United States in 1803. In the early 19th century, many migrants fleeing the Haitian Revolution arrived in Louisiana, bringing with them Haitian Vodou, which contributed to the formation of Louisiana Voodoo. Practiced primarily by black people, but with some white involvement, Voodoo spread up the Mississippi River to Missouri. Although the religion was never banned, its practice was restricted through laws regulating when and where black people could gather. Growing government opposition in the mid-19th century brought multiple arrests and prosecutions, while increased press attention directed greater attention to prominent Voodoo practitioners like Marie Laveau. Voodoo died out in the early 20th century, although some of its practices survived through hoodoo.

Information about Voodoo's beliefs and practices comes from various historical records, but this material is partial and much about the religion is not known. Historical records reveal the names of various deities who were worshiped in Voodoo. Prominent among them were Blanc Dani, the Grand Zombi, and Papa Lébat, whose identities derived from various African divinities. These were venerated at altars and offered animal sacrifices; several sources refer to the involvement of live snakes in rituals. Spirits of the dead and Catholic saints also played a prominent role. Each Voodoo group was independent and typically led by a priestess or less commonly a priest. Membership of these groups was provided through an initiation ceremony. Major celebrations occurred at Saint John's Eve (23 or 24 June), which in the 19th century was marked by large gatherings on the shores of Lake Pontchartrain. Also playing an important part of Voodoo practice was the production of material charms, often known as gris-gris, for purposes such as healing and cursing.

Louisiana Voodoo has long faced opposition from non-practitioners, who have characterized it as witchcraft and devil-worship, negative attitudes that have resulted in many sensationalist portrayals of the religion in popular culture. From the 1960s, the New Orleans tourist industry increasingly used references to Voodoo to attract visitors, while the 1990s saw the start of a Voodoo revival, the practitioners of which drew heavily on other African diasporic religions such as Haitian Vodou and Cuban Santería.

Louisiana Voodoo was a religion, and more specifically an "African diasporic religion", an African American religion, and a creole religion. Louisiana Voodoo has also been referred to as New Orleans Voodoo, and—in some older texts—Voodooism. The scholar Ina J. Fandrich described it as the "Afro-Creole counterculture religion of southern Louisiana".

Louisiana Voodoo emerged along the Mississippi River valley, and especially in the city of New Orleans, during the 18th and early 19th centuries before dying out in the early 20th century. It was informed heavily by the traditional African religions brought to the region, predominantly from West Central Africa and Senegambia, but also took influence from the Native Americans of the Mississippi River Valley, French and Spanish settlers, Anglo-Americans, and Haitian migrants bringing with them Haitian Vodou.

The historical record for Voodoo is fragmentary, with much information about the religion being lost and not recoverable. It was a largely oral tradition, with its followers often being illiterate or uninterested in committing information about their practices to writing. It had no formal creed, nor a specific sacred text, and had no unifying organized structure or hierarchy. Practitioners often adapted Voodoo to suit their specific requirements, in doing so often mixing it with other religious traditions. Throughout its history, many Voodoo practitioners also practiced Catholicism and integrated Catholic elements into their practice of Voodoo. In turn, the Catholic Church largely ignored Voodoo throughout much of the 18th and early 19th centuries. The prominent 19th-century Voodoo priestess Marie Laveau for instance regularly attended Mass at a Catholic church, and was close friends with the Catholic Friar Antonio de Sedella, who worked with her in ministering to the sick.

The term Voodoo derives ultimately from vodu, a term meaning "spirit" or "deity" among the Fon and Ewe languages of West Africa. Although the spelling Voodoo is now the most popular way of referring to the Louisiana religion, variant spellings have been used over the years, including Voudou and Vaudou. In modern scholarship, the spelling Voodoo is sometimes used for the Louisiana practice to distinguish it from Haitian Vodou. When the religion was active, its practitioners often referred to themselves as Voodoos, although elsewhere they have been called Voodooists.