The long-standing challenge of string theory, confronting the real world, has become more pressing and at the same time tangible in view of the upcoming LHC. Since the low energy limit of the theory is the main stage where predictions can be compared with experimental data, the goal of this project is to develop a new unified framework to formulate, compute and analyze this limit and its phenomenology. Understanding the low energy limit of string theory at the level where it can be confronted with precision experiments requires two key elements. On one hand one must obtain the full low energy Lagrangians resulting from compactifications from ten to four dimensions. On the other hand, one must analyze the couplings of quarks and leptons, represented by open strings attached to branes. Attempts to construct four-dimensional effective theories have focused in the past on a particular class of six-dimensional spaces, but my work in the last few years has shown that realistic solutions arise from manifolds whose differential properties are actually much weaker and that these compactifications have an elegant reformulation in terms of a generalized version of Riemannian geometry. I plan to use the formalism of generalized geometry to obtain the full tree level, perturbative and non-perturbative corrections to the 4D LEEL resulting from compactifications on these manifolds, and to study their phenomenology. Obtaining the full LEEL is the key step towards understanding if the world as we see it today comes from a string theory compactification: only full knowledge of the Lagrangian allows us to determine in detail how these manifolds lead to theories having 4D isolated vacua with a tiny positive cosmological constant, and support branes whose gauge theory spectrum and couplings are those of the Standard Model. Furthermore, the LEEL will be compared with the data of tomorrow: masses and couplings of supersymmetric partners, if supersymmetry is found at the LHC.