Quantum states of mechanical resonators promise access to completely new experimental regimes of physics: from unprecedented levels of force sensitivity to the generation of macroscopic quantum superpositions of massive objects containing up to 10^20 atoms. This opens up not only exciting possibilities for novel applications but also allows to (re)address fundamental questions of quantum physics, in particular its relation to the classical world. For this reason the preparation and control of mechanical quantum states has long been an enticing but far fetched goal of breakthrough character. With the advent of micro- and nano-mechanics this goal is at the verge of becoming an experimental reality. The last few years have witnessed unprecedented global progress in pushing mechanical systems towards the quantum regime. A thriving interdisciplinary field has emerged that aims to exploit the tremendous potential that lies in the control of mechanical quantum states. The main idea of this proposal is to combine the tools and concepts of quantum optics with micro- and nano-mechanical systems. Such combination provides a unique and powerful approach that allows, with a minimal set of experimental interactions, universal quantum control over mechanical systems via opto-mechanical interactions. The feasibility of the approach has recently been verified by us and by several other groups worldwide in a series of experimental demonstrations of mechanical laser cooling. The main objective of the proposed research is to go significantly beyond the current state-of-the-art and to develop the field of quantum-opto-mechanics to its full extent, both in experiment and theory. This will also increase the European visibility in this highly topical area of research. My professional background in both solid-state physics and quantum optics and quantum information will be of additional help in this highly interdisciplinary endeavour.