In human beings teeth are diphyodont. Two sets of teeth develop and erupt at different period of time during life. Primary or deciduous or milk teeth erupt from 6 months to 24 months of age. Permanent teeth erupt from 6 years to 24 years of age. Tooth develops from two sources ectoderm and mesoderm. This chapter covers the time of eruption of primary teeth and time of eruption of permanent dentition. From 6 months to 24 months, primary teeth erupt in the order following as mandibular central incisors, maxillary central incisors, lateral incisors, first molars, canines, and second molars.