Covalent organic frameworks (COFs) are a novel class of porous crystalline organic materials assembled from molecular building blocks. The construction principles of these materials allow for the design of precisely controllable structures since their chemical and physical properties can be easily tuned through the selection of the building blocks and the linkage motif. Their extraordinary and versatile properties impart functionality that is of great interest in areas such as gas storage, separation, catalysis and optoelectronics. This feature article discusses key aspects of the design of covalent organic frameworks with a focus on electroactive COFs for potential optoelectronic and photovoltaic applications.