A complete three-dimensional picture of the partonic structure of nucleons requires to step beyond the standard collinear approximation in high-energy processes, with the introduction of Transverse-Momentum Dependent (TMD) parton distribution and fragmentation functions. TMDs can reveal unprecedented information about spin-momentum correlations in non-perturbative QCD and help, in particular, in answering the question of the origin of the spin of the nucleon. During the last ten years, pioneering advances have opened up a broad vision of this multidimensional landscape and we are now entering a transition phase from explorative investigations to the precision mapping of partonic structure in momentum space.
 
I will summarize the most significant aspects of the phenomenological study of TMD physics, focusing on semi-inclusive deep inelastic scattering processes and hadronic production in lepton-lepton annihilations.