We use ESA/Gaia astrometry together with SEGUE and LAMOST measurements of the GD-1 stellar stream to explore the improvement on the Galactic gravitational potential that these new data provide. Assuming a realistic universal model for the dark matter halo together with reasonable models of the baryonic components, we find that the orbital solutions for GD-1 require the circular velocity at the Solar radius to be V_circ_(R_{sun}_)=244+/-4km/s, and also that the density flattening of the dark halo is q_rho_=0.82^+0.25^_-0.13_. The corresponding Galactic mass within 20kpc was estimated to be M_MW_(<20kpc)=2.5+/-0.2x10^11^M_{sun}_. Moreover, Gaia's excellent proper motions also allowed us to constrain the velocity dispersion of the GD-1 stream in the direction tangential to the line of sight to be <2.30km/s (95% confidence limit), confirming the extremely cold dynamical nature of this system.