The experimental study of transition to detonation has been enhanced recently by two novel techniques. One exploits simply the fact that a self-sustained detonation front, unlike any other wave associated with the transition process, is capable of leaving imprints on the wall along which it travels. The other is based on the adaptation of an amplitude modulated, giant pulse, laser system as a light source for stroboscopic schlieren photography. The insight gained by the utilization of these techniques into the wave processes accompanying the onset of detonation is unparalleled in the long history of the study of these phenomena. The results demonstrate that the transition can take place in various modes depending on the wave interaction processes which occur ahead of the accelerating flame.