Understanding the fundamental relationship between atomic structure and material properties is the holy grail of the science of materials. Towards this goal we are working to develop a real-time and atomistic understanding of the mechanistic steps taken during the growth and transformation of crystalline materials. To do this we employ a combination of complementary synthetic and characterization approaches, in particular using in situ ultra-high resolution transmission electron microscopy (TEM) to observe key structural transformations in real-time. Our in situ experiments include directly performing nanomaterial synthesis in the TEM as well as determining the kinetics of structural phase transformations of as-synthesized inorganic nanocrystals. Further, based on an unexpected observation made during one of these in situ measurements, we have developed a new approach to directly synthesize arrays of crystallographically well-defined nanoscale interfaces. Several examples will be presented to illustrate our approach, including: the real-time observation of the solid-state reaction of an individual nanowire; a post-synthetic structural phase transformation within an individual nanorod, and finally, the creation of new nanostructured architectures using liquid metal nanodroplets.