Einstein’s GTR initiated a new programme for describing fundamental interactions, in which the dynamics was described in geometrical terms. After Einstein’s classic paper on GTR (1916c), the programme was carried out by a sequence of theories. This chapter is devoted to discussing the ontological commitments of the programme (Section 5.2) and to reviewing its evolution (Section 5.3), including some topics (singularities, horizons, and black holes) that began to stimulate a new understanding of GTR only after Einstein’s death (Section 5.4), with the exception of some recent attempts to incorporate the idea of quantization, which will be addressed in Chapter 11. Considering the enormous influence of Einstein’s work on the genesis and developments of the programme, it seems reasonable to start this chapter with an examination of Einstein’s views of spacetime and geometry (Section 5.1), which underlie his programme.