Cancer still imposes a global threat to public health. After decades of research on cancer biology and enormous efforts in developing anticancer therapies, we now understand that the majority of cancers can be prevented. Bioactive phytochemicals present in edible plants have been shown to reduce the risk of various types of cancer. Ginseng (Panax ginseng C.A. Meyer), which contains a wide variety of saponins, known as ginsenosides, is an age-old remedy for human ailments, including cancer. Numerous laboratory-based studies have revealed the anticancer properties of ginsenosides, which compel tumor cells to commit suicide, arrest the proliferation of cancer cells in culture and inhibit experimentally-induced tumor formation in laboratory animals. Ginsenosides have been reported to inhibit tumor angiogenesis, as well as the invasion and metastasis of various types of cancer cells. Moreover, ginsenosides as combination therapy enhance the sensitivity of chemoresistant tumors to clinically used chemotherapeutic agents. This review sheds light on the molecular mechanisms underlying the cancer chemopreventive and/or chemotherapeutic activity of ginsenosides and their intestinal metabolites with particular focus on the modulation of cell signaling pathways associated with oxidative stress, inflammation, cell proliferation, apoptosis, angiogenesis and the metastasis of cancer cells.