A protein complex is a group of two or more proteins that interact with each other to perform a specific biological function. These complexes can be found in various cellular processes, such as cell signaling, gene expression, and metabolism. The interactions between proteins in a complex can be temporary or stable, depending on the function they serve. Protein complexes can vary in size and composition, often including additional molecules like nucleic acids or lipids. Understanding these complexes is crucial for studying how cells operate and can provide insights into diseases when these interactions go awry.