The past decade and a half has witnessed the discovery of a large, evolutionarily conserved family of cellular genes bearing homology to the prototype baculovirus Inhibitor of Apoptosis (IAP). The logical decision in the field to also refer to these cellular proteins as IAPs fails to do justice to this versatile group of factors that play a wide range of roles in eukaryotic development and homeostasis which include, but are not limited to, the regulation of programmed cell death. Here we describe the shared functional characteristics of several well-characterized IAPs whose defining motifs place them more in the category of multifunctional modular protein interaction domains.