Protein interactions are the foundation of cell biology. For robust signal transduction to occur, proteins interact selectively and modulate their behavior to direct specific biological outcomes. Frequently, modular protein interaction domains are central to these processes. Some of these domains bind proteins bearing post‐translational modifications, such as phosphorylation, whereas other domains recognize and bind to specific amino acid motifs. Other modules act as diverse protein interaction scaffolds or can be multifunctional, forming head‐to‐head homodimers and binding specific peptide sequences or membrane phospholipids. Additionally, the so‐called head‐to‐tail oligomerization domains (SAM, DIX, and PB1) can form extended polymers to regulate diverse aspects of biology. Although the mechanism and structures of these domains are diverse, they are united by their modularity. Together, these domains are versatile and facilitate the evolution of complex protein interaction networks. In this review, we will highlight the role of select modular protein interaction domains in various aspects of plant biology. The ability for proteins to interact is central to their biological functions. Modular protein domains act as a biological toolkit that allow evolution of protein interactions. In this review, we provide a snapshot of how individual domains drive protein versatility and lay the groundwork for complex protein interactions in plants.