Today's miniature devices and biological systems share the fact that their dynamics and properties cannot be understood, in terms of macroscopic concepts, but require a thorough understanding of the nanoscale structuring This structuring is often very heterogeneous both in time and in space, and is difficult or impossible to resolve with traditional approaches. In this Progress Report, we will discuss how single-molecule microscopy - and defocused wide-field field imaging in particular-can be used to shed light on these phenomena.