With fluorescence microscopy, we visualize soluble proteins, organelles and structures like the nucleus, or the border between mother and daughter cell. Prerequisite for fluorescence microscopy is the existence of a fluorophore. We use often the green fluorescent protein or its derivatives to make proteins visible. In the image shown here, histones in the two yeast mating types are tagged with different fluorescent proteins a blue and a red fluorescent protein. The tagging with a fluorescent protein allows microscopy of living cells also for a time period.