Our research interests are in the atomic-resolution investigation of functional nano-materials and their defects. For this purpose we use aberration-corrected electron microscopy techniques to investigate atomic and electronic defect structures for a subsequent correlation with nano-scale and macro-scale physical properties of the materials. In addition to this rather traditional approach to the structure-property relationships, we use and develop in situ electron microscopy techniques to study the evolution of atomic-scale defect structures under applied stress, such as electrical and mechanical fields, (rapidly) varying temperatures, etc. Studying materials under conditions closer to their anticipated working environment allows the detailed systematic investigation of their functionalities. Our overreaching vision is the in operandi observation of functional nano-materials with atomic resolution and precision.