Marker-assisted introgression (MAI) is one of the major applications of molecular information in animal breeding aiming at introgression of one or more favorable genes from a line (donor) to another (recipient), while keeping the genetic background of the recipient as much as possible. It consists of three phases. Firstly, cross donor and recipient lines to produce F₁; secondly, repeated backcross the F₁ individuals and the subsequent progenies with the recipient to recover its genetic background; and thirdly, intercross the backcrossed progenies to fix the introgressed genes in the population. Many factors affect the efficiency of MAI, among which the methods of foreground and background selection are very critical.