Does a photoreaction have a kinetic order? Thus far, this basic question has no clear answer in the literature. Most often, photochemical reactions were treated by the classical thermal kinetic models set out for 0th-, first- or second-order kinetics. Even if a debate was shortly held about this issue to justify the relevance of thermal kinetic orders for photoreactions, the controversy was not definitely settled. Hence, today, whether a primary photoprocess has a particular kinetic order or whether it should simply obey a thermal order is not a fully resolved issue. This chapter will succinctly review the scarce literature around that opening basic question.