Published in 1882 by Siegbert Tarrasch, 'The Blue Book of Chess' (originally 'Chess Midgame Principles') is a classic work on chess strategy. It's considered one of the first serious attempts to systematically analyze chess middlegame positions based on positional factors rather than just tactical combinations. The book focuses on principles like pawn structure, piece activity, control of the center, king safety, and prophylaxis (preventing the opponent's plans). It uses a collection of master games from the mid-to-late 19th century (players like Steinitz, Tarrasch himself, Capablanca, Lasker, etc.) as practical examples to illustrate these strategic concepts. While not a tactical manual (though it includes some), it lays down enduring principles that shaped modern strategic thinking.