The embryonic origin and histological organisation of the insertion periodontium, formed by the cementum, the periodontal ligament and the alveolar bone, is explained here. You will see that the three tissues are formed during the development of the tooth root from the ectomesenchymal cells of the dental sac. You will learn that cementum is a mineralised tissue very similar to bone, although several types of cementum can be distinguished, in some of which there are no cells. You will see that, unlike bone, cementum does not usually remodel and is very resistant to resorption. You will learn that the periodontal ligament is a connective tissue with groups of collagen fibres running through it, from the alveolar bone to the cementum. Finally, you will study that the alveolar bone is odontodependent and you will see that different sides can be distinguished and the organisation of each one.