The Reverse Phase Protein Array (RPPA), a high-throughput antibody-based microarray with procedures similar to Western blots, is a super sensitive and precise technology for the quantitative measurement of hundreds of target proteins in both preclinical and clinical samples. This array format enables the quantification of numerous proteins or phosphoproteins in multiple samples under the same experimental conditions simultaneously. Furthermore, it is well-suited for signal transduction profiling of small numbers of cultured cells or cells isolated from human biopsies, including formalin-fixed and paraffin-embedded (FFPE) tissues. Due to its simplified sample preparation (compared to mass spectrometry-based technologies) and its exceptional sensitivity for detecting low-abundance signaling proteins across a wide linear range, RPPA holds significant potential for characterizing deregulated interconnecting protein pathways and networks using limited sample amounts.