In the world of Mouse Guard, mice struggle to live safely and prosper amongst harsh conditions and a host of predators. Thus the Mouse Guard was formed: more than just soldiers, they are guides for common mice looking to journey without confrontation from one village to another. They see to their duty with fearless dedication so that they may not simply exist, but truly live.
Mouse Guard is a game of anthropomorphic mice, but it's not cute. It's about people struggling to make a difference for good in a hostile and dangerous world. It's about stepping up and being a hero when the easy thing is to run and hide.
The rules are straightforward when you understand them, but are not well explained in the book (the rules tend to be scattered throughout the book). For my ease of reference, I wrote a crib sheet for the rules.