In this talk, space-time finite element methods will be presented as an approach to solving PDEs with time-dependence. In these methods, time is treated in the same way as the spatial variables, leading to a fully unstructured finite element discretization in space-time. The fundamental properties of this approach will be discussed, especially in contrast to the Method of Lines. In particular, the efficiency of space-time methods on massively parallel computers will be discussed, as well as the importance of this property in modern numerical software.