Precision measurements are an integral part of particle physics. They are essential for determining free parameters of the Standard Model (SM), and also for searching for signals of new physics beyond the SM. Apart from collider results from LEP, Tevatron, and the LHC, the increasing role is being played by precision measurements performed at much lower energies, well below the weak scale. In this talk I will review the place of nuclear beta transitions in this program. Thanks to the improving accuracy of experiment, theory, and lattice calculations, the precision level of beta transitions is reaching order 10^-4 in some cases. In particular, beta decays offer the most precise determination of the Vud element of the CKM matrix, which may hint at new physics due to the so-called CKM unitarity problem. I will describe the wide spectrum of current and planned experiments, and how they improve our understanding of the SM and non-SM physics.