This book represents the first compilation of the major research findings regarding Maspin—a mammary serpin (or serine) protease inhibitor. Maspin was originally discovered through subtractive hybridization and differential display analyses, comparing the differences in gene expression in normal mammary epithelium and invasive carcinoma cells. This work originated in the laboratory of Dr. Ruth Sager, a world-renowned geneticist, at the Dana Farber Cancer Institute and Harvard Medical School. The first introduction of Maspin to the research community occurred as a report in Science (v263:526-529, 1994), and described the unique tumor-suppressing activity of this novel gene in human mammary epithelial cells.