A detergent composition suitable for washing fabrics is in the form of a stable oil-in-water microemulsion and comprises an organic surfactant system, preferably wholly or predominantly consisting of ethoxylated nonionic surfactant, a non-aqueous solvent, and a water-soluble polymeric detergency builder. Preferably the surfactant system comprises an ethoxylated nonionic surfactant having an average alkyl chain length of less than C12. The composition can be used both for pre-wash treatment and as a main wash detergent.