With well over 200,000 documented species (Mora et al., 2011) flowering plants (angiosperms) are among the most successful taxa on the planet. A major reason for the success of the angiosperms is self-incompatibility, a genetic and biochemical barrier to inbreeding that promotes outcrossing and diversity in populations. Plants exhibiting selfincompatibility have the ability to recognize (species-specific) pollen as being “self” or “nonself”, with self (incompatible) pollen being rejected and non-self (compatible) pollen being accepted. S-RNase-based Gametophytic Self-Incompatibility (GSI) has been characterized in the Solanaceae, Rosacaeae, and Plantaginaceae (McClure et al., 2011; Meng et al. 2011; Chen et al., 2010; Sims & Robbins 2009), with the genetic, physiological and molecular basis of this form of GSI described in detail. To date, over a dozen different proteins have been identified that function in different parts of the GSI response; most of these have been tested for protein interactions with other GSI response pathway proteins. The two key recognition proteins: S-RNase (the style-expressed recognition component) and SLF (the pollenexpressed recognition component) interact with each other, and with other components of a putative SCFSLF E3 ubiquitin ligase complex. Recently Kubo et al., 2010 demonstrated the existence of multiple SLF variant classes. Multiple S-RNase and SLF alleles are present in breeding populations (Richman et al., 1995, 1996, 2000), and it now seems probably that collaborative interaction of different SLF alleles and classes with different S-RNase alleles governs self/non-self recognition in GSI. In this review, I summarize the genetic basis of GSI, describe the different proteins identified that are thought to function in the GSI pathway, and describe what is known with regard to protein interactions underlying the function of self-incompatibility. Most of the work discussed here comes from studies in the Solanaceae and Plantaginaceae. Gametophytic self-incompatibility has also been studied extensively in the Rosaceae (e.g. Sassa et al., 2010). Work that demonstrates possible differences in the mechanism of GSI in Solanaceae/Plantaginaceae versus Rosaceae will be discussed as appropriate.