The increased use of antibodies as therapeutics, as well as the growing demand for large numbers of antibodies for high-throughput protein analyses, has been accompanied by a need for more specific antibodies. An array containing every protein for the relevant organism represents the ideal format for an assay to test antibody specificity since it allows the simultaneous screening of thousands of proteins in relatively normalized quantities. Indeed, the use of a yeast proteome array to profile the specificity of several antibodies directed against yeast proteins has recently been described. In this chapter, we present a detailed description of the methods used to probe protein arrays with antibodies as well as the technical issues to consider when carrying out such experiments.