The molecular mechanisms of signaling network molecules and dynamics are important topics in cell biology research. SH2 and SH3 are small scaffold molecules functioning in protein-protein interactions to mediate signal transduction pathways that are activated by protein kinases. In plants, several studies have uncovered the novel functions of SH2 or SH2-like domain containing proteins that are similar to the signal transducers and activators of the transcription (STAT) family. The Arabidopsis thaliana genome also contains SH3 domain-containing proteins (SH3Ps), but little is known about their functional roles in plant development and growth. In this chapter, we will summarize and discuss the evolutionary conservations of the plant SH2 and SH3 domain proteins with particular emphasis on their roles in regulating signaling transduction and membrane trafficking in plant cells.