The concession agreement for the modernization and operation of Indira Gandhi International airport in Delhi and Chhatrapati Shivaji International airport at Mumbai respectively is referred to as Operation Management and Development Agreement (OMDA). The OMDA was a part of a set of transaction documents along with the request for proposal provided to potential bidders. The OMDA laid out the contractual terms for structuring the PPP. This paper discusses the evolution of the draft OMDA from when it was first released in April 2005 to the bidders till it was released as a final OMDA in August 2005 before an extended bidding date. During this period, some of the critical issues addressed were: limits to commercial development of airport land, nature of tariff regulatory regime, contingent liabilities including performance bonds and termination payments, and potential contractual and strategic conflicts. It brings out the intra-governmental issues and processes, and the significant learning that formed part of these PPP concessions, which could well be among the largest in the world.