This paper reviews certain structural aspects of the periodontal ligament. These include collagen (type, crimping and fibril diameters), ground substance (functions), cells (fibroblast morphology, cell heterogenicity and distinguishing of cell phenotypes, cell kinetics, ‘foetal’ characteristics), nerves (presence of neuropeptides) and blood vessels (presence of fenestrations). Attention is drawn to recent advances in our understanding of the development of the periodontal ligament, especially cementum formation, and in the presence of bioactive molecules such as growth factors and cytokines.