Dye chemistry was one of the initial topics of chemical research in the academicas well as industrial field. At the early stage of dye research, in the last decades ofthe 19th and the beginning of the 20th century, the focus was on the elucidationof structures of natural dyes aiming at the development of their chemicalsyntheses and to establish theoretical concepts for the understanding of thecolor–constitution relationship as a prerequisite for the design of new artificialcolorants. The major outcome of these pioneering efforts for mankind was thatcolor is no more a privilege of nature and, hence, multi-colored paints enteredour everyday life and textiles of any desirable shade became accessible.Nowadays most colorants have the purpose to satisfy our aesthetical needsand, thus, thousands of dyes and pigments are produced on industrial scales.Nevertheless, nearly periodically new demands arise for so-called “functionaldyes” whoseπ-conjugated systems exhibit novel functionalities beyond aes-thetical purposes. Optical brighteners or near-infrared absorbers are exampleswhere even transparency in the visible spectrum is desired and dyes for non-linear optics, holographic optical data storage and two photon absorptionare further examples where the color properties of “dyes” are insignificantlyrelated to the functional demands. Each chapter begins with an outline, abstract, and set of key words and ends with a ‘forward look’ that provides suggestions for further studies in the field. In summary, this book complements earlier ones in the field pertaining to functional dyes in general and supramolecular assemblies specifically.