Material selection is discussed. The data rate of orthoferrites, garnets, and magnetoplumbite devices, for example, are compared. Also reviewed is the status of propagation circuits. The bubble is examined from the viewpoint of its use as a vehicle to obtain material data. A new method to measure domain-wall mobilities is introduced. This method, which is based on the dynamics of a collapsing bubble, permits measurements to be made over a wide dynamic range.