This volume, the fourth of the quantum probability series, collects part of the contributions to the Year of Quantum Probability organized by the Volterra Center of University of Rome II. The intensive communication among researchers during this Year allowed several open problems to be solved and several inexpected connections to be revealed.

This volume, the fourth of the quantum probability series, collects part of the contributions to the Year of Quantum Probability organized by the Volterra Center of University of Rome II. The intensive communication among researchers during this Year allowed several open problems to be solved and several inexpected connections to be revealed.