From the Introduction:
Great & Small (G&S for short) is a role-playing game of animal fantasy, in which you and your friends take on the roles of intelligent animals in a world full of dangers. You create your own stories, in a sort of make-believe-with-rules game, and spin tales of your characters' adventures and intrigues. A role-playing game is like you and your friends writing your own novel or movie, with yourselves in the roles of the main characters.
Each player assumes the role of a nonhuman, real-world animal who can talk and think in a manner similar to humans, except for one player, who takes the role of the game's referee, called the Beast Master. The Beast Master, or BM for short, comes up with the challenges the other players' characters face, describes the actions and situations to them, and handles the roles of enemies or supporting characters they may interact with. The players and the BM work together to tell a story about their characters, using game rules to resolve conflicts or other situations in which the outcome is uncertain.
The rules for Great & Small are based on a classic fantasy role-playing game created by Gary Gygax and David Arneson, and also pay homage to another early table-top RPG that was inspired by the novel Watership Down. Some of you may have played the original fantasy game before, and if so, many of the rules here will seem very familiar to you. For other players, this may be your first exposure to the concept of role-playing games. Either way, the rules are designed to be simple and easy to understand.