In analogy with their inorganic counterparts, crystalline organic semiconductors have the advantages of uniform well-defined electronic and optical properties, as well as improved charge carrier mobility, owing to band-like transport and fewer traps, compared to amorphous films. Advances in processing techniques have led to better prospects and increasing interest in organic devices based on crystalline materials, including organic field effect transistors (OFETs), organic light emitting diodes (OLEDs), organic photovoltaics (OPV), photodetectors, and scintillators. The properties of crystalline organic semiconductors can be tuned in many ways, including chemical substitution and side-group functionalization, which can modify the molecular properties as well as the crystal packing, promoting the crystallization of polymorphs with different properties, co-crystallization, and doping. This opens up a vast design space with endless possibilities for devices based on crystalline organic semiconductors.