This handbook, published by Chroma Technology, is a comprehensive compilation of principles, design, and terminology related to optical filters used in fluorescence microscopy. It serves as an invaluable guide for researchers to understand the critical role of filters in achieving high-quality fluorescence imaging. The handbook covers fundamental concepts such as excitation and emission spectra, the function of dichroic mirrors, and the various types of filters (e.g., bandpass, longpass, neutral density) and their applications. It delves into the technical aspects of filter design, including thin-film coatings and optical quality parameters, and discusses how filters can affect the optical alignment of a microscope. It provides practical knowledge for designing filters for a variety of fluorescence microscopes, including wide-field and confocal systems, and for applications involving simultaneous detection of multiple fluorescent probes. The guide also includes a glossary of terms, making complex concepts accessible. This resource is essential for anyone involved in fluorescence microscopy, from optimizing existing setups to designing new experiments, ensuring a thorough understanding of the optical components that are vital for signal purity and image contrast.