Through weak lensing and galaxy clustering measurements, the next generation of large-scale surveys (Euclid, LSST, ...) will provide unprecedented observations and constraints on the late Universe, and thus shed light on dark matter and dark energy. On the other hand, high-quality CMB observations (current and planned) can -- and already do -- put tight constraints on the early Universe and its content. Combining these two sources of cosmological information and exploiting their existing correlations can yield a significant lever arm and improve tremendously the constraints on our cosmological model, especially its non-standard extensions. In this talk, I will present an overview of my work on the topic of the joint analysis of LSS and CMB data and its potential, both from a theoretical standpoint and a practical one in the context of international collaborations (Planck, Euclid).