Arjen K. Lenstra & Hendrik W.Jr. Lenstra 
Development of the Number Field Sieve [PDF ebook] 

The number field sieve is an algorithm for finding the prime factors of large integers. It depends on algebraic number theory. Proposed by John Pollard in 1988, the method was used in 1990 to factor the ninth Fermat number, a 155-digit integer. The algorithm is most suited to numbers of a special form, but there is a promising variant that applies in general. This volume contains six research papers that describe the operation of the number field sieve, from both theoretical and practical perspectives. Pollard’s original manuscript is included. In addition, there is an annotated bibliography of directly related literature.