This volume will help readers understand our current views concerning the answers to these questions as well as frame new questions that will be answered by the European Space Agency's satellite that was launched in late 2013. The book contains the elaborated notes of lectures given at the 42 Saas-Fee Advanced Course “Dynamics of Young Star Clusters & Associations" by Cathie Clarke (University of Cambridge) who presents the theory of star formation and dynamical evolution of stellar systems, Robert Mathieu (University of Wisconsin) who discusses the kinematics of star clusters and associations, and I. Neill Reid (S