The largest issue facing the sector is the treatment and discharge of oily wastewater. Fats, oils, greases, and dissolved organic and inorganic compounds in suspension make up oily wastewater. In improving the water quality related to the removal of oily wastewater, various treatment techniques designed to remove oil contaminants can be applied. Before discharging wastewater into water streams, effective oily wastewater treatment is crucial to enhancing the quality of the wastewater in accordance with wastewater discharge requirements. The chapter describes the overview of oily wastewater and its treatment technologies. The chapter also explained the different emulsion types found in the industries. Moreover, issues and challenges faced by the industries to treat oily wastewater are also highlighted. Among the other technologies, two technologies, membrane technology and chemical treatment, have been discussed in detail. © 2023 Elsevier Inc. All rights reserved.