In this Research News article we discuss the significance of dimensionality on the charge-transport properties of organic semiconductors. Dimensionality is defined in two ways: as a function of (i) the π-conjugated framework within the molecular structure, and (ii) the degree and direction of intermolecular close-contacts between molecules in the bulk. In terms of dimensionality, silicon is a good role model for organic semiconductors, since it demonstrates 3D architecture in the bulk through covalent bonding. Achieving this for organics is challenging and requires not only a 3D molecular structure, but also a network of intermolecular short contacts in three dimensions. This review identifies the limitations of low dimensional materials and summarizes the challenges faced in progressing towards fully 3D organic semiconductors.