Definition: A type of microscopy that uses light of an appropriate  wavelength to stimulate fluorescence in a sample. The emitted fluorescence is then used to produce an image. The imaging device can be your eye, a camera with film, or a CCD camera. These "wide-field" imaging devices (eyes and cameras) see the entire field of view at once. A diagram of how epifluorescence works is below. The arrangement of the apparatus as shown uses epillumination to induce fluorescence, which is why this form of microscopy is termed "epifluorescence" microscopy.

In this diagram, an excitation light source produces light having many different colors. An excitation filter removes all colors of light except those which will be used to cause the sample to fluoresce. The dichroic beam splitter (mirror) reflects the shorter wavelength blue light down through the objective lens and onto the specimen. Fluorophore molecules in the specimen emit fluorescence which passes up, through the objective lens, through the dichroic mirror to be detected by eye or a camera. The barrier filter just above the dichroic mirror makes sure that only selected wavelengths are detected. Numbers associated with the filters are the center wavelength and the number of nanometers that are passed around the center wavelength. I.e.: a 475 / 30 filter is centered at 475 nm and passes light from 460nm to 490nm.