Significant research has been done on the straightforward but hotly debated topic of catalytic oxidation of carbon monoxide (CO), i.e., \(2\text{CO}+{\text{O}}_{2}\to 2{\text{CO}}_{2}\) on surfaces of metals or metal oxides. Carbon monoxide is one of the toxic gas pollutants emitted mainly by the incomplete burning of fossil fuels. The surfaces of transition metal atoms and/or their oxides demonstrate their potential use in CO oxidation. As one of the most well-known heterogeneous reactions, CO oxidation can be used as a benchmark system. In this regard, the surface chemistry and catalytic effectiveness of the metals and their oxides with/without atomically dispersed active sites and/or oxygen defects have been investigated in significant experimental and computational studies. The present chapter describes the experimental and theoretical studies conducted on the oxidative removal of carbon monoxide (CO) over transition metal catalysts. To avoid complexity, this chapter covers literature reported since 2017.