In this animation, we will introduce you to fluorescence microscopy. Fluorescence microscopy is a special type of light microscopy in which the microscope uses a laser as the light source. A researcher will require the use of fluorescent microscope to visualize autofluorescent cellular structures, fluorescent dyes or stains, or to analyze the expression, modification, and our localization of proteins using fluorescent antibodies by a technique called immunofluorescence. In a fluorescence microscope, the light source travels in a different trajectory than in the basic light microscope that we illustrated in the microscopy experimental technique animation. Instead of the laser light being transmitted through the sample as an assembled bright field based light microscope, the fluorescence microscope uses incident or reflected light. From the laser light source, the excitation laser beam travels through the filter cube, which is used to provide the appropriate wavelength of light to excite the fluorescent molecules or fluorophores, used in the sample, then through the objective to focus the laser light on the sample. The light emitted from the sample is then reflected back through the objective and the filter cube, which filters the emitted light to the camera or eyepiece where the researcher can view the fluorescent signal. One advantage to fluorescence microscopy is that it can be used to detect and visualize multiple fluorescent molecules by simply adjusting the excitation and emission filters to detect the relevant fluorophores in a sample. Fluorescent microscopy also has many useful applications in the laboratory setting. Fluorescent dyes or stains are used to detect cellular structures. One example of a commonly used fluorescent dye is DAPI, which binds to DNA, and a second example is Faloidin, which binds to F-Actin. Expression modification and or localization of specific proteins can also be visualized using immunofluorescence, or IF. Like immunohistochemistry, IF uses multiple steps to detect specific proteins using antibodies in the sample. In IF, one of the antibody labeling steps utilizes fluorescently tagged antibodies that are detectable upon excitation using the appropriate wavelength of light.