The use of ionic liquids as solvents or catalysts has a notable impact. As a result, there is increasing interest in developing applications for them in a variety of synthetic reactions. The purpose of this chapter was not to be entirely complete, but rather to summarise some of the most recent advances in the use of ionic liquids in organic synthesis as a catalyst. The present chapter focuses on a general introduction to green and sustainable chemistry, as well as how it relates to homogeneous catalysis. A brief history of ILs as homogeneous catalysts is presented, various along with preparative routes and applications. Starting with their application, ILs have been used as catalysts in a variety of organic reactions. This focuses on the synthesis, significance, and applications of ILs. Although they are not particularly useful as solvents, they are now being used as catalysts in organic chemistry catalytic reactions.