In the context of pharmaceutical development, it is abundantly clear that there is a need for greater understanding and control of crystalline phases. The field of crystal engineering is poised to address such issues and has matured into a paradigm for the supramolecular synthesis of new compounds with desired properties. Crystal structures are unpredictable by nature, however, the interactions that lead to crystal formation are becoming much more predictable. By means of model compound studies, the delineation of the hierarchy of hydrogen bonding between complementary functional groups or supramolecular heterosynthons can be accomplished. Competitive co-crystallization studies along with data extracted from the Cambridge Structural Database (CSD) can be utilized in understanding the reliability of supramolecular heterosynthons without the need for endless co-crystallization experiments. In effect, this ability to understand supramolecular heterosynthons can allow crystal engineers to rationally design co-crystals with a high rate of success. It has been suggested that pharmaceutical co-crystals could play a significant part in the future of API formulation since in principle they will outnumber pharmaceutical salts, polymorphs and solvates combined. The focus of this thesis is the understanding of the primary amide functional group and its hydrogen bonding capabilities; as well as the synthesis of model compounds in order to develop a blueprint for the design of pharmaceutical co-crystals using APIs that contain a primary amide functional group.