Cancer is a deadly disease characterized by abnormal cell growth and the ability to spread or invade other parts of the body. It can affect different parts or organs of the body such as lungs, breasts, pancreas, skin, and blood. Nature is endowed with a variety of products that have pharmaceutical properties and they are found in abundance. Majority of the anticancer drugs are derived from natural sources. The ocean is home to various organisms and is also a primary source of multiple biological compounds. Varieties of marine-derived compounds have the potential for being used in therapeutic and pharmaceutical research. Marine ecosystems are a significant and largely untapped source of possible anti-cancer drugs. Marine compounds have antiviral, antibacterial, antifungal, anticancer, antidiabetic, and anti-inflammatory properties. Some marine-derived drugs fight excessive proliferation by inhibiting cell division through receptor-mediated growth signaling. Marine organisms, such as tunicates, mollusks/cyanobacteria, fungi, sponge, and bacteria are the major sources of anticancer compounds. This book contains a detailed explanation of the various therapeutic properties associated with marine compounds. It will serve as a reference to a broad spectrum of readers.