The realm of transition metal-catalyzed direct arylation via C–H activation has undergone significant advances in recent years. It has been established as a viable alternative to the standard cross-coupling reaction with organometallic reagents. The use of directing moieties, often through coordination to the catalytic metal, enhances the reactivity and regioselectivity of the C–H activation. In this chapter, the contribution of transition metals such as palladium, rhodium, ruthenium, iridium and copper is discussed. Mechanistic aspects, including the roles of the potential directing groups and of other additives, are emphasized. This chapter serves a concise summary along with essential information that could be beneficial for further understanding and development.