Covalent organic frameworks (COFs) are newly emerged crystalline porous polymers with well-defined skeletons and nanopores mainly consisting of lightweight elements linked by dynamic covalent bonds. This chapter discusses the evolution of COFs and highlights the important issues related to synthetic method and structural design. The crystallization of COFs has generally been dominated by kinetically controlled reactions that form irreversible covalent bonds. Higher reversibility, that is, dynamic covalent chemistry, must be achieved for efficient error correction. Thermodynamic products have in common COF chemistry of the amorphous products initially obtained until the synthetic conditions are optimized by varying the crystallization time, reaction temperatures, reaction solvents, and catalysts. The design of methodologies to precisely control pore size and distribution to achieve a large surface area is a central theme in the exploration of porous materials containing COFs. Most COFs are prepared via the solvothermal (ST) synthesis method. A typical ST condition for the synthesis of COFs is as follows.