Covalent organic frameworks (COFs) have become a versatile platform to immobilize a wide variety of single-atom metal catalysts. The resulting post-synthetic modified materials present a spectrum of valuable properties ranging from homogeneous to heterogeneous systems, such as well-defined catalytic sites, selectivity, recyclability, and stability. In this minireview, we discuss selected contributions that provide experimental and computational details on reaction mechanisms (e. g., via EXAFS, TEM, and DFT) catalyzed by single-atom metals embedded within the COF structure. When applicable, we highlight the different behaviour between molecular (homogeneous) and COF-supported (heterogeneous) sites regarding catalytic performance. With this survey, we aim to decipher the key features that aid in seeing COFs as not merely passive supports but as active items in catalysis.