Optical microscopy is a powerful tool for examining the microscopic and nanoscopic world. In many areas of science, including biology and the fabrication of new (sub)-micron structured materials, the optical microscope is an indispensable tool. Over the last two decades, the field of nonlinear optical microscopy has added new imaging capabilities that are of tremendous impact for biology and material sciences. The technique of four-wave mixing (FWM), in particular, has shown great potential as an imaging method that is able to probe material properties that have remained inaccessible using conventional techniques. Coherent anti-Stokes Raman scattering (CARS) microscopy, a FWM technique, is gained a lot of momentum as a biological imaging tool. CARS is sensitive to both the vibrational and electronic properties of materials. In this thesis, we have applied CARS microscopy to two distinct areas: biological tissue imaging and characterization of nanowires. Our study of the lipid distribution of meibomian glands highlights the vibrational sensitivity of the CARS technique. We have extend the current state-of-the-art by developing hyperspectral CARS imaging, which generates images with spectral information, and combined this with principal component analysis (PCA), a multivariate analysis technique. The results of this study provide a new look at the lipid distribution in meibomian glands, and, by linking structure to functionality, it provides clues towards the origins of dry eye disease. In a second study, we have explored the electronic sensitivity of CARS microscopy. Electronic CARS was used to interrogate the nonlinear optical properties of semiconducting nanowires. This study has revealed the optical anisotropy of polycrystalline CdSe nanowires, which offers new insights into the optical response of such nanoscopic systems. Finally, we have used our microscope system to improve the optical properties of nanowires. We have developed a laser zone annealing method for increasing the grain size of polycrystalline nanowires. Our results demonstrate that the optical and electronic properties of selected segments of the nanowire can be significantly improved.