With the increasing complexity of modern air warfare, an efficient and robust mission planning, which mainly includes task assignment and path planning, becomes the key issue to improve the combat efficiency. This paper reviews recent progress in UAV mission planning. First, basic concepts of UAVs and their mission planning problem are given. And several representative existing mission planning systems are briefly introduced. The constraints and objectives in the task assignment model are reviewed, and the pros and cons of algorithms commonly used are then summarized. After that, the algorithms for path planning are reviewed. Finally, we point out current problems and future research directions. The paper provides a comprehensive review of the field and enables a quick start for those who aim to do related research.