As mentioned previously, the models that make up a Warhammer army must be formed into 'units' before battle commences and all units must adopt a formation. The core rules cover in detail Close Order formations, which are by far the most commonly seen – but by no means the only – type of formation.

The following sections introduce the rules for Open Order and Skirmish formations. These are the two most frequently seen unusual formations, and every army will have the option to include units that can adopt them. A wise general will make full use of such units to exploit terrain, to harass the enemy from unexpected quarters and to protect their own vulnerable flanks.