Abstract: In this talk, I will present work on relating transverse momentum dependent (TMD) and collinear factorization formalisms in a generalized framework. I will focus on the case of transversely polarized observables such as the Sivers effect. I will also discuss the validity of the well-known relations, such as between the weighted TMD Sivers function and the collinear twist-3 Qiu–Sterman function, and their use in phenomenological studies of the 3-D structure of hadrons.