Humanitarian engineering involves the application of engineering to improve the well-being of marginalized people and disadvantaged communities, often in low- and middle-income countries of the world. This text examines humanitarian engineering as applied to the needs of oncology (cancer) care. In the next two decades the number of new cancer cases around the world will increase by more than 50% over the present levels, driven largely by increases in countries with transitioning economies. Huge inequities exist. How will these challenges be met? This text presents foundational principles, as well as case studies from various oncology disciplines including radiation oncology, one of the most technologically complex specialities which involves the controlled use of radiation to treat cancer. Oncology care presents a major global challenge and humanitarian engineering offers one pathway forward.