A selective systemic herbicide used pre-emergence to control annual grasses and many broadleaf weeds among vegetables, maize, soybeans and nuts — classified by WHO as slightly toxic. Concerns about groundwater contamination and its classification as a probable human carcinogen led the European Union to ban it, with other regions restricting or phasing it out. Residue monitoring in cereals and drinking water continues where it remains approved. Alachlor’s trajectory from workhorse to restricted substance traces the modern arc of pesticide regulation: effective chemistry reassessed as toxicology and environmental monitoring improve.