A universal mechanism of the Boson peak formation in glasses is proposed. The mechanism is based on the concept of interacting quasi-local oscillators. Even in the case of weak interaction the low-frequency spectrum becomes unstable. Due to anharmonicity the system undergoes a transition into a new stable configuration. Below some characteristic frequency the renormalized density of states becomes a universal function of w with a Boson peak feature, i.e. the reduced density of states g(W)/W**2 has a maximum at a frequency Wb << Wc. We derive an analytical form of this function.