Light microscopy: an ongoing contemporary revolution

The optical microscope is one of the oldest scientific instruments that is still used in forefront research. Ernst Abbe's nineteenth century formulation of the resolution limit in microscopy let generations of scientists believe that optical studies of individual molecules and resolving subwavelength structures were not feasible. The Nobel Prize in 2014 for super-resolution fluorescence microscopy marks a clear recognition that the old beliefs have to be revisited. In this article, we present a critical overview of various recent developments in optical microscopy. In addition to the popular super-resolution fluorescence methods, we discuss the prospects of various other techniques and imaging contrasts and consider some of the fundamental and practical challenges that lie ahead.