Protein array technology is becoming an increasingly important tool in the drive toward proteome-scale analysis of protein activity and interactions. Presently, this technology compliments the more traditional methods for proteomic analysis, including two-dimensional gel electrophoresis/chromatography and mass spectrometry. While the task of producing a “whole-proteome” chip, containing active proteins, is a daunting one, current protein and antibody arrays represent the first steps toward that goal. In this review, we discuss current approaches for the generation of protein arrays, and their applications, including their use in the study of protein–protein, protein–nucleic acid, enzyme–substrate, and so on, interactions. Potential applications of protein arrays in interaction screening, such as compound–protein interactions are also discussed.