The syntheses of porous crystalline materials and their related application have drawn significant attentions in the fields of chemistry, physics, and materials science, where metal-organic frameworks (MOFs) and covalent organic frameworks (COFs) are two notable classes of reticular materials with unique structures. MOFs are built via coordination bonds between metal clusters or ions and organic linkers, while COFs are formed by networking pure organic units with covalent linkages. However, MOFs and COFs each have own shortcomings according to their linkage nature. For example, MOFs, due to the relatively weak coordination bonds, often suffer from rather low chemical stability, limiting their practical application. In contrast, COFs are highly stable under harsh conditions because of their strong covalent bonds, but the lack of open metal sites hinders the further application of COFs. To overcome these limitations, a new type of crystalline porous material, namely, covalent metal-organic frameworks (CMOFs), has been synthesized by combining the chemistry of MOFs and COFs. CMOFs are expected to have unique structural complexity and exceptional functionality. In this chapter, recent progresses on CMOFs, including the design of metal cluster/complex, linker and topology, control of stacking structure and morphology, and potential applications, are summarized. Additionally, the promising prospects and challenges in the CMOF-based research area are also discussed.