A portfolio of swaps that are held by a swap dealer. In the early days of the swap market, banks took on the role of swap brokers, arranging swaps between end users in exchange for commissions from both. That changed in the early 1980s when banks began to intermediate between the counterparties to a swap, dealing with each counterparty on a separate basis. And hence came the shift from swap brokers to swap dealers. Dealers take and hold position in swaps through a process called swap warehousing (positioning). In other words, a dealer warehouses a portfolio of swaps or is said to be running a swap book.

Swap dealers work off their swap books to customize a swap to meet the requirements of counterparties. To that end, they may undertake a portion of a swap in order to consummate a transaction. Thereafter, they try to offset their swap books by entering into another swap or portion of a swap. In addition to other swaps, a swap book can be hedged using futures contracts or bonds.