The single largest source for this tradition is a collection of interviews. Harry Middleton Hyatt recorded thousands of hours with practitioners and clients across the American South from the 1930s onward and published the transcripts at enormous length, largely unedited. The result is a record in the speakers' own words of what was done, what it cost and who did it, and it remains the foundation of serious study of the practice.
The distinction that most needs making is between hoodoo and the religions it is often confused with. Hoodoo is a body of practical workings: protection, luck, love, court cases, healing, and the undoing of harm done by others. It has no pantheon, no initiation and no priesthood, and the great majority of its practitioners have been Christians who saw no conflict, using psalms and biblical verses as working material. Vodou in Haiti and Vodun in West Africa are religions, with deities, initiated priesthoods and liturgies. Conflating them is both inaccurate and, in the popular press, usually pejorative.
Its sources are African, Native American and European in mixture, with a substantial layer drawn from the Bible, and it was shaped by the conditions of slavery and its aftermath, in which recourse to law and medicine was frequently unavailable.
By the early twentieth century a supply trade had grown around it, with mail-order houses selling oils, powders and roots to a national market. Some of that trade was run by people outside the communities that used it.