The Art of War is the main book of reference when we talk about military strategy. There are other titles that are regularly used by military academies and business schools, but we can say that Sun Tzu is the main point of reference. It was written 2400 years ago and it summarizes Asian warfare in a way that has influenced and guided famous generals to this day.
The Official Edition has the best translation out there, done between several scholars from the universities of Shanghai, Hunan, and Liverpool two or three years ago. It is commercialized by Shanghai-Hunan Publishing through different retailers worldwide.