Apoptosis as a form of programmed cell death is a critical defense mechanism against the formation and progression of cancer and exhibits distinct morphological and biochemical traits. In an in vivo situation, apoptosis functions to eliminate potentially deleterious cells without causing such adverse effects as inflammatory response and ensuing scar formation. Therefore, targeting apoptotic pathways becomes an intriguing strategy for the development of chemotherapeutic agents. Marine natural products have become an important source in the discovery of antitumor drugs, especially when modern technology makes it more and more feasible to collect organisms from seas. Although lack of an analog of a long ethno-medical history for finding clues, as compared with terrestrial habitats, still hinders the progress, an increasing number of compounds have been isolated from marine organisms that have been found to possess apoptosis-inducing and anticancer activities. This primer summarizes several such compounds, based on their effects on apoptotic signaling pathways, although most of these products have not yet been studied in depth for their mechanisms of action.