Almost all the quantum systems are inevitably coupled with their surroundings, which brings two-fold effect: dissipations and fluctuations. Understanding the open quantum many-body system is a topic of fundamental interest in various fields of physics and challenging both the theorists and experimentalists. Even though dissipation and noise-induced decoherence are detrimental for almost all the quantum-based experimental devices and techniques, from the theoretic point of view, the open quantum many-body system itself is fundamentally different from the traditional Hamiltonian systems, and provides a new perspective to the quantum many-body physics. In the first part of the talk, I will give an example of a natural generalization of the spin-boson model to the many-spin case, where I will show that dissipation can qualitatively change the properties of the quantum many-body systems, and give rise to novel quantum phases and phase transitions. In the second part, we will show that the conspiracy of interaction and noise can give rise to universal long-time dynamics: an algebraic decoherence behavior with infinite-long decoherence time, which is fundamentally different from the conventional exponential decoherence behavior in single particle quantum systems.