This lecture explains how hydrogen bombs---also called thermonuclear bombs, fusion bombs, or h-bombs---work. The key innovation is to build multiple stages. In a Teller-Ulam configuration, a boosted implosion device makes up the primary stage. The weapon then directs the energy created to a secondary stage, which consists of hydrogen and further nuclear fuel. The fusion, along with additional fission, from the secondary stage creates a substantially larger explosion than a normal nuclear weapon.