Stability at the nano-scale Catherine Brechignac Laboratoire Aime Cotton CNRS Universite Paris-sud, FRANCE Control of matter on the nano-scale already plays an important role in scientific disciplines as diverse as physics, chemistry, materials science, and biology. However, the first fundamental question which rises following the preparation of nano-objects is: Are these objects stable? Studying their fragmentation is one of the keys to understand their stability. Even though quite general concepts can effectively describe various aspects of fragmentation processes at different length-scale, at the nano-scale the instabilities leading to fragmentation may considerably influence the morphology of the nano-objects. Moreover, the fascinating capability that a nano-object has to modify its shape in order to minimize its free energy leads to shape modifications that may be observed on a reasonable time scale. These issues will be discussed in light of several examples, specifically: cluster fission and nano-fractal thin film fragmentation.