To get insights into the molecular interactions that take place in cells and tissues, fluorescence microscopy appears nowadays as the most powerful and common way to proceed. Advances in fluorescent fusion proteins such as green fluorescent protein (GFP), chemical dyes and nanoparticles provide the biologist with a rich labeling kit that is at the very basis of fluorescence microscopy. Although extremely powerful, fluorescence comes with a number of questions that cannot always be answered, the most dramatic one being to which extent a fluorescent label — often bigger than the biomolecule of interest — will affect the complex molecular interaction at work in cells and tissues? Furthermore labeling or staining often relies on complex bio-chemistry and is not always possible. Clearly, developing label free microscopy techniques as alternatives to fluorescence is important.