The ability to image beyond the diffraction limit is the central tenet of the burgeoning field of superresolution fluorescence microscopy, also referred to as optical nanoscopy. The advent of superresolution has revolutionized biological fluorescence microscopy and the field at large. However, much of that excitement has been tempered by prohibitive imaging requirements. Achieving superresolution entails certain sacrifices, namely imaging speed, choice of fluorophore, ease of multicolor and three-dimensional imaging, and generally more complex instrumentation as compared to standard widefield imaging techniques. Several techniques utilizing structured illumination occupy an intriguing middle ground between the ease of use associated with traditional fluorescence microscopies and the unprecedented resolving power of modern superresolution methods, resulting in undeniably robust imaging techniques. Presented here is a review of the conceptual basis of structured illumination and its implementation, including its performance in comparison to other nanoscopies and the most recent developments in the field.