Adsorption is one of the most widely used water treatment technologies because of its simplicity, ease of operation, and flexibility in removing many types of pollutants, and commercial activated carbon holds a leading position among adsorbents. However, its high production cost, and the fact that it is usually manufactured from fossil sources such as coal, have pushed researchers to look for cheaper and more sustainable alternatives. Agricultural waste is an attractive option for several reasons: it is abundant, renewable, and cheap or free, and it consists mainly of cellulose, hemicellulose, and lignin, polymers that carry functional groups (hydroxyl, carboxyl, and phenolic) capable of binding pollutants. Valorizing it also solves two problems at once, waste disposal and water treatment, which is consistent with the principles of the circular economy. In countries where date palms are widely grown, such as Iraq, date pits, palm fronds, and palm fiber represent locally available raw materials of particular interest, alongside corn, barley, and rice residues. Agricultural activities generate enormous quantities of biomass waste, such as cereal straw, rice husks, sugarcane bagasse, date pits, and citrus peels, most of which is burned or left to decompose without being put to use. Meanwhile, water bodies suffer from growing contamination by heavy metals, dyes, pesticides, and pharmaceuticals. This article examines the potential of converting agricultural waste into low-cost adsorbents for wastewater treatment. It reviews the types of raw materials and the methods of preparation and activation, the adsorption mechanisms, the equilibrium and kinetic models used to describe adsorption, and the factors affecting efficiency. It then discusses the challenges that hinder the transition to real-world application, including variability of raw materials, regeneration, and disposal of spent adsorbent, and concludes with future research directions. 2. Agricultural Raw Materials The agricultural raw materials used to prepare adsorbents can be classified as follows: • Woody and fibrous residues: corn and rice straw, corn cobs, sugarcane bagasse, and palm fronds. • Shells and hard husks: rice husks, and walnut, almond, and pistachio shells, as well as olive and date pits. • Soft peels: orange, lemon, banana, and pomegranate peels, which are rich in pectin and carboxyl groups. The composition of each material differs: lignin-rich residues usually yield a more stable char, while rice husks contain a high proportion of silica, which affects pore structure and adsorption behavior.