Src Homology 3 domains are found ubiquitously throughout the known proteome. Because they have no catalytic activity and are able to bind specific peptide sequences containing a PXXP motif, they are thought to be used generally as coupling domains. While the significance of some SH3 mediated protein interactions may be slight, others have a great deal of importance. Namely, SH3 domains are thought to be responsible for binding mechanisms involved in regulating activity in some enzymes. The Tec family of protein tyrosine kinases each contain a single SH3 domain. Additionally, four of the members, Tec, Btk, Itk and Rlk include at least one polyproline peptide sequence known to bind SH3 domains. We have explored some of the characteristics of the interactions between these SH3 domains and their respective proline ligands. Specifically, ligand affinity and ligand availability were considered as possible mediating factors in binding. Our data suggests that the affinity of a polyproline ligand for its SH3 domain is a major factor in determining whether the interaction is intra- or intermolecular. Findings presented here lay a foundation for future work in probing regulatory mechanisms by SH3 domains.