A Century of Quantum Mechanics

In October 2011 we celebrated the centenary of the Solvay conferences that played a unique and important role in the development of twentieth century physics, most notably in the quantum revolution whose birth overlapped the initiation of these meetings. The centenary conference was entitled the Theory of the Quantum World. I shall present the opening address that I gave at this conference, in which I summarize the state of our theoretical understanding of the quantum world and the conceptual challenges that we face.