Over the past century, our understanding of cells—the basic building blocks of living organisms—has progressed largely due to microscopes. The invention of fluorescence microscopy has been a primary tool in this scientific endeavor because it allows researchers to color-label specific cellular components and observe them in live cells. The new two-color 3-D Minflux microscope is a vast improvement on traditional fluorescence microscopy because, for the first time, researchers can track how two molecules can interact with each other on the size scale of the molecules themselves.