The Holy Grail of fundamental physics research today is to find and describe a theory that explains, at least in principle, all physical phenomena. What happened exactly on, or even before, the Big Bang? Where are we coming from and where are we going? Questions that have never been addressed before by physicists. This book contains articles by leading physicists describing the current situation. Among them are proponents as well as opponents of string theory, and proponents of other ideas such as Loop quantum gravity, commutative geometry, and others.