Circulating Tumor Cells (CTCs), shed into the bloodstream from primary and metastatic tumors are regarded as the liquid biopsy of cancer is an enthusiastic field of research which attracted half-a thousand publications in the recent two decades. The Circulating Tumor Cells research can be categorized into three major aspects: 1) Clinically focused on the applications of Circulating Tumor Cells as biomarkers for cancer diagnosis, progression, prognosis and therapeutics; 2) Molecular characterization of Circulating Tumor Cells to determine their clinical relevance and functional activities in tumor microenvironments; and 3) Technological investment in detection and isolation of rare Circulating Tumor Cells from peripheral blood specimens and even in vivo tracking of Circulating Tumor Cells.