This talk deals with the dynamic facilitation approach to the glass transition problem. This perspective is based on the idea that the interesting structure in glass-forming systems is found in the space of trajectories of the dynamics, rather than that of configurations. In contrast to mean-field approaches, dynamic facilitation naturally accounts for the dynamic heterogeneity of glass-forming materials and related fluctuation phenomena such as transport decoupling. I will describe how in the d+1 dimensions of trajectory space one finds order-disorder phenomena that can be organized according to scaling and universality classes. Various predictions from this viewpoint, some yet to be verified experimentally, will be discussed.