Ofele and Wanzlick reported the synthesis of the first N-heterocyclic carbene (NHC) metal complexes in 1968.1,2 The isolation of the first free carbene by Arduengo in 1991 set the scene for an ever-growing interest and advancement in the field of N-heterocyclic carbene chemistry.3 Shortly thereafter, the use of these ligands in organometallic chemistry, particularly in catalysis dramatically increased.4,5 N-heterocyclic carbenes are neutral 2-electron donors, with an ability to bond to both hard and soft metals making them more versatile ligands than phosphines.6 As an added advantage, not only are NHCs easier to synthesize and functionalize than phosphines but they also form a stronger bond to metals and therefore form more stable metal complexes than metal phosphine complexes.7,8 The N-heterocyclic carbene ligands interact with metal centers primarily through strong σ-donation and to a lesser degree through π-backdonation (Figure 1).9,10 Figure 1 Orbital diagram of NHC bonding to metal center. Ghosh and coworkers11,12,13,14,15,16 as well as others17,18,19 took special interest in the exceptional stability of several metal-NHC complexes and conducted in depth analyses in order to gain better insights into the structure and bonding. In particular, the metal-ligand donor-acceptor interactions were inspected using the charge decomposition analysis (CDA). CDA is a tool used to quantitatively estimate the degree of NHC → metal σ-donation, designated by d, and NHC ← metal π-back donation, designated by b.20,21 Thus a higher d/b ratio emphasizes the ability of NHC to function as an effective σ-donor, whereas a lower d/b ratio highlights the greater NHC ← metal π-back donation. Interestingly, in the studies conducted by Ghosh, greater NHC ← metal π-back donation was observed in Pd-NHC complexes exhibiting lower d/b ratios ranging between 2.59 – 3.9913,14 and Au-NHC complexes with d/b ratios ranging between 5.23 – 5.8815,16 as compared to the Ag-NHC complexes with d/b ratios ranging between 7.8 – 12.6811,12,16. This observation could attest to why silver-NHC complexes are particularly better transmetallating agents. The newly emerging interest in the medicinal applications of stable metal NHCs led us to examine the few accounts available in the literature dealing with this area of research. This review will discuss in detail the medicinal applications of various transition metal-NHC complexes including silver, gold, rhodium, ruthenium, and palladium. The antimicrobial, antitumor, and resistance properties, along with proposed mechanisms of action to suppress the bacterial growth or proliferation of tumor cells will be discussed.