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Connecting organic building blocks by covalent bonds to design porous crystalline networks has led to covalent organic frameworks (COFs), consequently transferring the flexibility of dynamic linkages from discrete architectures to extended structures. By virtue of the library of organic building blocks and the diversity of dynamic linkages and topologies, COFs have emerged as a novel field of organic materials that propose a platform for tailor-made complex structural design. Progress over the past two decades in the design, synthesis, and functional exploration of COFs in diverse applications successively established these frameworks in materials chemistry. The large-scale synthesis of COFs with uniform structures and properties is of profound importance for commercialization and industrial applications; however, this is in its infancy at present. An innovative designing and synthetic approaches have paved novel ways to address future hurdles. This review article highlights the fundamental of COFs, including designing principles, coupling reactions, topologies, structural diversity, synthetic strategies, characterization, growth mechanism, and activation aspects of COFs. Finally, the major challenges and future trends for large-scale COF fabrication are outlined.