Traditional cancer chemotherapy relies on the premise that rapidly proliferating cancer cells are more likely to be killed by a cytotoxic agent. In reality, however, cytotoxic agents have very little or no specificity, which leads to systemic toxicity, causing severe undesirable side effects. Therefore, various drug delivery protocols have been explored. Tumor cells overexpress many receptors and biomarkers, which can be used as targets to deliver cytotoxic agents into tumors. In general, a tumor-targeting drug delivery system consists of a tumor recognition moiety and a cytotoxic warhead connected directly or through a suitable linker to form a conjugate. This book discusses the design and development of a novel series of the second-generation taxoid conjugates with ?-3 polyunsaturated fatty acids; and a new class of disulfide-containing linkers for tumor-targeting prodrugs. This book should help shed some light on the exciting research of directing therapeutics to tumors, and should be especially useful to professionals in anticancer drug discovery and delivery fields.