Abstract: In this seminar, I would like to talk about the spontaneous symmetry breaking (SSB) in dissipative systems. The difference between SSB in closed and open systems are strongly emphasized. For the case of continuous SSB, the Goldstone theorem and Ward-Takahashi Identity in the open system can be obtained by the non-equilibrium quantum field theory, which described the dissipation of the condensate order parameter to the quantum fluctuations and the phase diffusion. For the case of the discrete symmetry, the evolution of the system is described by the master equation, which shows the similar physics in the system with continuous symmetries. I will show some examples. e.g., the laser generation and the optical parametric system, to give the intuitive picture for the SSB in open systems.