Gene targeting in the mouse is an essential technique to study gene function in vivo. Multigene families encoding vomeronasal receptor (VR) type 1 and type 2 consist of ~300 intact genes, which are clustered at multiple loci in the mouse genome. To understand the function of VRs and neurons expressing a particular VR in vivo, individual endogenous receptor genes can be manipulated by conventional gene targeting to create loss-of-function mutations or to visualize neurons and their axons expressing the VR. Multiple receptor genes in a cluster can also be deleted simultaneously by chromosome engineering, allowing analysis of function of a particular VR subfamily. Here, we describe protocols for conventional gene targeting and chromosome engineering for deleting a large genomic region in mouse embryonic stem (ES) cells.