We discuss the operator definition of the transverse momentum dependent parton distribution/fragmentation functions (TMDs). We present TMD operators in the completely (ultraviolet and rapidity) renormalized form suitable for straightforward evaluation of any matrix element. We show the consequences following from operator definition, such as renormalization group equations and small-$b_T$ operator product expansion. This methodology was successfully applied to unpolarized TMD distributions, where all perturbative quantities were calculated at NNLO. The obtained perturbative parts are important for any kind of phenomenology involving TMDs.