Tooth agenesis constitutes the most common anomalies of dental development in man. Despite this, little is known about the genetic defects responsible for this complex condition. To date, the only genes associated with the non-syndromic form of tooth agenesis are MSX1 and PAX9, which encode transcription factors that play a critical role during tooth development. This paper aims to review current literature about the molecular mechanisms responsible for selective tooth agenesis in humans.