Marine oil spills have been of tremendous concern due to the adverse impact on economic and ecological systems. Major oil spills such as the 2010 Deepwater Horizon oil spill triggered worldwide consciousness of marine spill response. In past decades, significant advances have been made in diverse aspects including prevention and preparedness, spill response and cleanup options, modeling of marine oil spill, and response decision support; however, challenges still remain particularly associated with cold and harsh environmental conditions such as in the Arctic. This chapter provides a comprehensive review of marine oil spill preparedness and countermeasures, tackling topics such as preparedness and contingency planning, sensitivity and vulnerability, policies and regulations, cleanup technologies, oil trajectory and weathering modeling, early warning, response technology screening, net environmental benefit analysis, risk assessment, cleanup process simulation, and response decision-making. Knowledge gaps and technical challenges are also discussed indicating future research opportunities.