Experimental models of blastocyst development based on in vitro culture have played a prominent role in advancing our understanding of peri-implantation development, a process that is relatively inaccessible in vivo. Blastocyst culture provides a robust approach for examining embryonic interactions with the microenvironment under highly controlled conditions. Major events that occur in utero can be followed in vitro, including blastocyst expansion, hatching, and adhesion to extracellular matrices. This chapter will describe a method for obtaining and culturing mouse blastocysts. Morphological changes that occur during blastocyst culture will be discussed and related to the corresponding development in utero. Finally, quantitative assays will be detailed for monitoring peri-implanatation development of the trophoblast in vitro.