Next January will mark the fourth anniversary of President George W. Bush’s speech at NASA Headquarters that unveiled the Vision for Space Exploration, the long-term plan that gave the space agency a new direction, away from the space shuttle and space station and towards a human return to the Moon and, eventually, human missions to Mars. At that time the announcement drew comparisons to the Space Exploration Initiative (SEI), the last major effort by a president to reshape the direction of NASA, with corresponding concerns that the Vision would meet a similar, unfortunate fate. Yet the Vision is alive and well today (despite some concerns about its implementation), while SEI had effectively been dead long before it could reach its fourth anniversary. What caused SEI to fail, and what lessons did its failure provide future initiatives, like the Vision? These are questions explored in depth by Thor Hogan’s history of SEI, Mars Wars. The book (which can be ordered for $15 from NASA’s web site or read online for free) is, at its core, a thorough history of the SEI.