A book building that is used by an issuer to buy back shares from existing shareholders in the market. The underwriter solicits bids (reverse offers) from these shareholders and uses the order book to reach at a final offering price for the shares.

Reverse book building is a mechanism whereby an issuer can receive sell orders from the shareholders (usually, on an online basis) through a host of book running lead managers (BRLMs) in order to delist its shares through buy back transactions.

It is a sort of price discovery whereby an acquirer makes a delisting offer, quoting an indicative price at which the buy back process can take place. Then, investors of an issuer bid to sell their holdings of its share at a price they perceived to be fair. The price at which most of the investors bid to sell their shares forms the floor price, that would be used as a minimum level of the price in such transactions.