This chapter discusses the design and spectroscopic properties of laser dyes. After laser action was observed from chloroaluminum-phthalocyanine and 3,3'-diethylthiatricarbo-cyanine iodide about 30 years ago, thousands of compounds exhibiting fluorescence have been evaluated for laser action under flashlamp and nitrogen laser pumping. To continue fruitful development in this area, interest should ... [Show full abstract] be specifically focused on quasi-aromatic compounds. These are compounds comprising five-and six-membered heterocyclic systems. If a high Q F value is present, the compound should be tested for laser action under flashlamp excitation. If the Q F value is not too high, low, or zero, one should conduct spectroscopic studies to determine whether the compound exhibits low T-T absorption over the FSR. If this is the case, a closely related derivative may exhibit stronger fluorescence. Also, obtaining the T-T polarization spectrum may be helpful. Depending on the value of the degree of polarization recorded, substitution with interacting groups may result in efficient laser dyes.