Of the many markers for cancer stem cells (CSCs) in lung cancer reported to date, the cell surface antigen CD133, nuclear ss-catenin accumulation, the side population phenotype, and high aldehyde dehydrogenase (ALDH) activity seem to be most reliable. This book reviews the results of studies on lung CSCs and discusses the significance of these markers from a biological, pathological, and clinical viewpoint. Twenty-seven lung cancer cell lines (nine small cell lung carcinoma (SCLC) cell lines and eighteen non-small cell lung carcinoma (NSCLC) cell lines) were examined for mRNA and protein expression and fractions of cells with activity.