**5. Conclusions**

The imidazolium-based N-heterocyclic carbenes (NHCs) have found to be excellent candidates for improvising their properties through chemical modifications. Basic understanding and assessment of the steric and electronic factors of NHCs are crucial to explore its catalytic applications. Therefore, this chapter attempts to provide a basic glimpse of imidazolium-based NHCs through the discussions on some important synthetic routes, different methods for characterizing the electronic and steric properties of NHCs, and finally, few selective catalytic applications. Even though the literature pertaining to the imidazolium-based NHCs and its applications is vast and rapidly increasing, the discussions were limited to few important topics. Despite the extensive studies on imidazolium-based N-heterocyclic carbenes, there is plenty of scope for improvement, particularly enhancing the catalytic efficiency of NHCs with inexpensive metals, reducing the catalyst load, exploring new catalytic reactions with variety of substrates, and most significantly, making the NHC-based catalysts ready for more green and sustainable reactions.
