Abstract: LHCb has recently presented a measurement of R(J/Psi)=0.71(17)(18) in mild tension with the range of model predictions 0.25-0.28. The model transition form factors dominate the systematic uncertainty of the measurement and limit the predictions to a range of values. To improve this situation, we have undertaken to compute model-independent constraints on the transitions form factors via dispersive methods and lattice data. This allow for rigorous upper and lower bounds on R(J/Psi) to be computed in the Standard Model.