Warhammer 40k Kill Team Core Book (4th)

The book explains everything you need to play, including basic rules, weapon keywords, phases, actions, terrain for three separate Killzones (the vertical Volkus, watery Bheta-Decima, and confined Gallowdark), and provides two Mission Packs (the classic head-to-head Preliminary Ops pack and the new Joint Ops pack in which one or more players can play against the game itself, including full behaviours for a range of automatically controlled enemies known as Non-Player Operatives or NPOs)