The investigation of strong interactions at very high-energy has been the object of intense studies for many decades. Particularly interesting is the so-called Regge-Gribov (or semi-hard) limit of QCD, characterized by the scale hierarchy $s \gg \{Q^2\} \gg \Lambda^2_\textrm{QCD}$, where $\sqrt{s}$ is the center-of-mass energy, $\{Q\}$ a set of hard scales characterizing the process and $\Lambda_\textrm{QCD}$ is the QCD scale parameter. This limit is the stage where some of the most intriguing phenomena of QCD emerge. One such phenomenon is the saturation of the gluon density inside the proton, which leads to the formation of a state of hadronic matter characterized by a high density of particles and a disordered field distribution, known as the Color Glass Condensate (CGC).
In this talk, I will first review the basic concepts of perturbative QCD in its high-energy limit, emphasising the approaches developed to deal with gluonic saturation. Subsequently, I will use the paradigmatic example of diffractive processes to discuss the various theoretical challenges in reaching the precision frontier necessary to unambiguously unveil the gluon saturation dynamics at modern colliders.