Solid waste management has become a global problem as the rate at which waste is generated exceeds population growth. Although it is not the most environment friendly option due to the inevitable generation of greenhouse gases and leachate, landfilling is globally still the most commonly applied waste disposal method. Leachate, an extremely polluted wastewater, threatens ground and surface waters and requires adequate treatment before discharge. Co-treatment of leachate in municipal wastewater treatment plants (WWTPs) is a commonly practiced method for leachate management. However, changing characteristics of leachate and more stringent discharge limits in WWTPs have led to questions about sustainability of co-treatment. On the other hand, several new technologies and processes, which can be adopted in conventional WWTPs, are now being deployed. For instance, floccular activated sludge has evolved to granule processes, shortcut denitrification processes can potentially lower the oxygen and carbon requirement for nitrogen removal, membrane processes can provide higher effluent quality, more advanced aeration methods enhance energy efficiency, instrumentation, and control and automation capabilities have increased. This is the first dedicated review that compiles and critically evaluates studies concerning co-treatment of leachate and municipal wastewater. Moreover, potential concerns, challenges and opportunities for co-treatment are discussed in the context of new developments in wastewater treatment technology.