The purpose of this chapter is to update and complement a previous review article entitled “Egg Transfer”. 1 In that article, I discussed problems of egg transfer in general, and I outlined in detail the steps involved in the recovery of eggs from donors, their maintenance in vitro, and their transfer to recipients, in the rat. The egg transfer technique is essentially the same for rats and mice, with minor differences that will be pointed out later. The above-mentioned article was written and submitted in 1969; however, the book containing it was published in 1971. Although we are living in an era of rapid advances in science and technology, with the exception of nonsurgical transfers in mice, there have been practically no improvements in the technique of egg transfer in rats and mice. However, progress has been made in utilizing the egg transfer method. The present chapter is divided into two main parts: (1) technique and (2) applications.