One of the major environmental problems caused by the agro-food industry is the treatment of olive mill wastewater (OMW). OMW is a byproduct of olive oil production and is characterized by high concentrations of various organic compounds, including organic acids, pectin, and polyphenols, as well as inorganic compounds like sulfate, chlorides, and phosphoric salts of potassium and sodium, and trace amounts of other elements. These compounds make OMW complex and toxic to plants, inhibiting bacterial activity. Therefore, these compounds must be removed from wastewater before it is discharged into the environment. Many conventional treatment processes for OMW have been used, relying on physical, biological, and chemical methods. However, they have limitations and low efficiency in removing pollutants, as they only transfer pollutants from one stage to another. The ultimate goal of any treatment process is to achieve complete mineralization of pollutants, which can be achieved through the integration of appropriate processes. Over the years, many researchers have evaluated various combined treatment methods to enhance treatment efficiency and comply with environmental regulations regarding wastewater discharge. This review focuses on combined treatment methods for treated OMW. We analyzed preliminary results in the literature and discussed many parameters used to improve the process. Additionally, this review summarizes the combined processes according to their respective types, along with their benefits, drawbacks, and future prospects. It also summarizes the environmental impacts of treating OMW. In general, the results extracted from the literature review show that combined treatment processes have proven effective in treating OMW and should remain a focal point for the development of enhanced processes that can remove more pollutants in a single process. Display omitted •The review summarizes the performance of more than 54 combined processes in removing various pollutants from olive mill wastewater (OMW).•Combined processes are more convincing and efficient than single processes for OMW treatment.•The study found that combined chemical-chemical and chemical-biological treatment processes are OMW's most common and widely used combination treatments.•Fenton and coagulation/flocculation (C/F) methods are the best treatments to be integrated as combined methods.