Kriegsspiel is a genre of wargaming developed by the Prussian Army in the 19th century to teach battlefield tactics to officers. The word Kriegsspiel literally means "wargame" in German, but in the context of the English language it refers specifically to the wargames developed by the Prussian army in the 19th century. Kriegsspiel was the first wargaming system to have been adopted by a military organization as a serious tool for training and research.

It is characterized by high realism, an emphasis on the experience of decision-making rather than on competition, and the use of an umpire to keep the rules flexible and manage hidden information. After Prussia's impressive victory over France in the Franco-Prussian War, other countries began designing similar wargames for their own armies.

Most forms of Kriegsspiel involve at least two teams of players and one umpire gathered around a map. The map represents a battlefield. Each team is given command of an imaginary army which is represented on the map using little painted blocks. Each block represents some kind of troop formation, such as an artillery battery or a cavalry squadron. The players command their troops by writing their orders on paper and giving them to the umpire. The umpire will then read these orders and move the blocks across the map according to how he judges the imaginary troops would interpret and execute their orders. The outcomes of combat are determined either by simple mathematical calculations or the umpire's judgement.

By definition, a "wargame" is a strategy game that attempts to realistically represent warfare. The earliest wargames were invented in the German states around the turn of the 19th century. They were derivatives of chess, but the pieces represented real military units, cavalry, infantry, artillery, etc. and the squares were color-coded to represent different types of terrain.

These early wargames were not realistic enough to satisfy the military. The pieces were constrained to move across a grid in chess-like fashion: only a single piece could occupy a square, even if that square represented, say, a square mile, and the pieces had to move square by square. This, of course, did not represent how real troops maneuvered in the field. The grid system also forced the terrain to take unnatural forms, such as rivers flowing in straight lines and right angles.

In response to these criticisms, a Prussian nobleman and wargaming enthusiast named George Leopold von Reisswitz set out to develop a more realistic wargame wherein the units could move about in a free-form manner over more natural terrain.

Reisswitz first experimented with a table covered in a layer of damp sand. He sculpted the sand into a three-dimensional model battlefield, with hills and valleys. He used little wooden blocks to represent troop formations. The Prussian princes heard about Reisswitz's project and asked for a demonstration. He showed it to them in 1811, and they enthusiastically recommended the game to their father, King Frederick Wilhelm III.

Reisswitz did not want to present the king a table of damp sand, so he set about constructing a more impressive apparatus. In 1812, Reisswitz presented to the king a wooden table-cabinet. The cabinet's drawers stored all the materials to play the game. The cabinet came with a folding board which, when unfolded and placed on top of the cabinet, provided a gaming surface about six feet by six feet in size. Instead of sculpted sand, the battlefield was made out of porcelain tiles, upon which terrain features were depicted in painted bas-relief. The tiles were modular and could be arranged on the table surface to create a custom battlefield. The scale was 1:2373. Troop formations were represented by little porcelain blocks. The blocks could be moved across the battlefield in a free-form manner; dividers and rulers were used to regulate movement.