Metal hexacyanoferrates (MHCFs) and their composites are most emergent nanomaterials for water remediation due to their ease to synthesis, large surface-to-volume ratio, improved stability, high selectivity, enhanced adsorption capacity, improved ion-exchange capacity, and ion transport. MHCFs were first discovered with the synthesis of Prussian blue (PB). A comprehensive and state-of-the-art overview of the various methods utilized for the synthesis of MHCFs such as ultrasonication method, electrochemical method, co-precipitation method, hydrothermal method, and green synthesis method has been discussed. Furthermore, this book chapter explores the different types of MHCF composites like MHCF-polymer composites, MHCF-carbonaceous composites, and MHCF-metal oxide composites, and their application in removal of numerous contaminants includes heavy metal ions, radioactive ions, dyes, pesticides, and pharmaceutical waste. The chapter also entails future research directions and commercialization challenges.