We are working to develop a real-time understanding of the mechanistic steps taken during crystalline growth or transformation via a combination of complementary approaches which incorporate (1) knowledge gained from nanostructure syntheses we perform in the lab, with (2) in situ observations of key transformations implemented in real-time using ultra-high resolution transmission electron microscopy (TEM). Our in situ experiments include directly performing synthetic steps in the TEM, as well as determining the structural phase transformations of materials under post-synthetic processing conditions. 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.