The 4th Edition of the Guide for the Care and Use of Agricultural Animals in Research and Teaching (Ag Guide) builds upon and replaces previous versions of the Ag Guide published in 1988, 1999, and 2010. The Ag Guide comprises subject-oriented chapters covering subjects that pertain to all the agricultural animal species (chapters 1 to 5) and species chapters, which fall under the purview of the respective association(s) dedicated to the species (chapters 6 to 13). Each association appointed a senior editor to steer the revision of their respective species chapters and to collaborate with the senior editors from the other associations to guide the revision of the subject-oriented chapters.