The Earth’s ocean is its most significant feature. Taking up more than 70% of the Earth’s surface, our ocean is essential for life on this planet. It provides approximately 2/3 of the oxygen we breathe, and it helps control and regulate our climate. Life on this planet evolved in our ocean almost 4 billion years ago. The ocean has nurtured life ever since, to the point today that 25% of all species on this planet currently lives in the ocean, although scientists believe that we may have only discovered 10% of the ocean’s species diversity. This course uses an ecological perspective to review the extraordinary diversity of life in the ocean, ultimately examining the extraordinary diversity of marine mammals that act as apex predators in this fascinating ecosystem.