This volume presents a comprehensive overview on the drug discovery processes aimed at generating inhibitors for the treatment of malihnancies believed to be dependent on the gain of function of protein tyrosine kinases (RTKs). Specific topics include Src as a target for pharmaceutical intervention, JAK kinases in leukemias/lymphomas, platelet-derived growth factor, structural biology of PTKs, PI3-kinase inhibition, and phosphoproteomics in drug discovery and development.