There are many different aproaches available to making a DNA library – which simply is a collection of different DNA sequences containing variation in one or more positions. Each library generation method deals differently with a number of parameters, such as location of the mutations and the number of variants generated. In most circumstances, it is possible for multiple methods to deliver the same library at different cost, or different libraries at the same cost. The challenge then becomes in choosing a suitable method that delivers a suitable library for the application at hand.