Integrable boundary states are fascinating quantum states which can be defined for a wide range of integrable models. In the first part of the talk, I will give the definition of integrable boundary states in QFT and then discuss the generalizations to spin chains and 1D Bose gas. I will then discuss their important properties. As an example, I will discuss an intriguing state called crosscap state, which can be defined universally for all the aforementioned models. In the second part of the talk, I will present applications of integrable boundary states. These include quench dynamics in statistical mechanics and the computation of certain correlation functions in AdS/CFT correspondence.