A protein complex is a group of two or more associated proteins. Protein complexes are a form of quaternary structure. Understanding the functional interactions of proteins is an important research focus in biochemistry, often referred to as proteomics.

Many protein complexes are established, particular in the model organism Saccharomyces cerevisiae, a yeast. The discovery of protein complexes is now performed genome wide; the elucidation of most protein complexes of the yeast is undergoing.