Dye pollution from industries such as dyeing, textile, leather, cosmetics and pigments is of increasing concern, calling for advanced methods of wastewater remediation. Many techniques have been applied to treat such effluents, but adsorption remains the easiest, low-cost, effective and reliable strategies. The recent development of magnetic composites combines properties of both organic and inorganic components and is thus opening new applications for color removal. Here, we review the use of magnetic nanomaterials to adsorb dyes from aqueous solutions. We present sources of water contamination, actual technologies for wastewater treatment, the impact of dyes on health and the environment, dye removal methodologies, and the advantages of magnetic separation. We also discuss nanoparticle synthesis, results on magnetic nanomaterials for dye adsorption, and adsorption models.