The present work aims to provide a comprehensive review of the experimental studies focusing on municipal solid waste incineration fly-ash (FA) treatments that are required before the application of advanced processes aimed at their final reuse or safe disposal. The investigated pre-treatments are divided into three categories: (1) water washing/chemical leaching; (2) electrodialysis; and (3) thermal separation. Analysed aspects include: (1) process efficiency; (2) effect on FA physical–chemical characteristics; and (3) process applicability as a function of secondary FA treatment steps which are generally required for final disposal or reuse of the remediated waste. Investigations related to these elements allows a determination of the efficacy and the operational convenience of a specific pre-treatment to achieve a proper FA remediation level. A comparison of studies in the literature provides a thorough source and a useful basis for correctly addressing future experimental activities and research efforts. The discussion of the results provides the basis for the development of a suitable methodology to optimize the environmentally sustainable reuse or safer disposal of treated FA.