Ionic liquids (ILs) are environmentally friendly solvents and catalysts that are made up of ions that melt at temperatures below 100 degrees Celsius. Due to their favorable features, they were used in a broad range of reactions. A phase-transfer catalyst (PTC) is a type of heterogeneous catalysis that involves chemical reactions that occur when a reactant migrates from one phase to another where a reaction can proceed. High reaction specificity and transformations can be made easier with PTC reactions. PTC has been used in oxidations, alkylation, nucleophilic replacements, polymerizations, reductions, and other processes. In recent years, scientists have become more interested in employing ILs instead of traditional PTCs in biphasic reactions. Their cation architecture and chain length changes have been shown to have a substantial impact on their performance as PTCs. This chapter aims to discuss the role of ILs as phase transfer catalysis in organic synthesis.