In this Account our efforts are described to establish the benzo[b]quinolizinium ion, also known as acridizinium or 4a-azoniaanthracene, as a water-soluble surrogate of anthracene for the development of selective fluorescent probes. It is demonstrated with selected examples that especially the 9-aminobenzo[b]quinolizinium is a donor-acceptor dye with favorable absorption and emission properties and may be used as a versatile building block for fluorescent light-up probes and ratiometric probes.