The subject of this chapter is the relationship between modern cosmology and fundamental physics – in particular, general relativity as a theory of gravity on one side, together with its unique application in cosmology, and the formation of structures and their statistics on the other side. It summarizes arguments for the formulation for a metric theory of gravity and the uniqueness of the construction of general relativity. It discusses symmetry arguments in the construction of Friedmann–Lemaître cosmologies as well as assumptions in relation to the presence of dark matter, when adopting general relativity as the gravitational theory. A large section is dedicated to ΛCDM as the standard model for structure formation and the arguments that led to its construction, and to the role of statistics and to the problem of scientific inference in cosmology as an empirical science. The chapter concludes with an outlook on current and future developments in cosmology.