ConspectusMetal-organic frameworks (MOFs) and covalent organic frameworks (COFs), as emerging porous crystalline materials, have attracted remarkable attention in chemistry, physics, and materials science. MOFs are constructed by metal clusters (or ions) and organic linkers through coordination bonds, while COFs are prepared by pure organic building blocks via covalent bonds. Because of the nature of linkages, MOFs and COFs have their own shortcomings. Typically, the relatively weak bond strengths of coordination bonds lead to poor chemical stability of MOFs, which limits their practical implementations. On the other hand, due to the strong covalent bonds, COFs exhibit rather higher stability under harsh conditions, compared to MOFs. However, the lack of open metal sites restricts their functionalization and application. Therefore, it is hypothesized that the "cream-skimming" of MOFs and COFs would address these drawbacks and produce a new class of crystalline porous material, namely, covalent metal-organic frameworks (CMOFs), with unprecedented structural complexity and advanced functionality. The CMOFs reveal a new synthetic approach for the preparation of reticular materials. Specifically, metal ions are reacted with chelating ligands to assemble metal complexes or clusters with functional reactive sites (e.g., -CHO, and -NH