The informal sector has slowly come to gain recognition in the literature of development since the term was first applied by Keith hart. The present study has attempted to review the concept and the different connotations that informal sector has come to possess with the passage of time. Apart from the concept and definitions, the study has looked into the bearings that this sector has on employment, earnings, productivity and migration. Though the sector is often classified as marginalized and carried out on the sidelines of the economy, its potential for growth and contribution for sustaining livelihoods has confirmed its legitimacy as a viable sector of the economy.