Balmer emission from supernova remnant shocks represent a powerful tool to study the microphysics of collisionless shocks. In fact the superb resolution of optical images in the Halpha band allows one to resolve the shock structure with details which are impossible in any other wavelength. In particular the line width and the spatial profile of Balmer lines reveal the physical conditions at the shock like the temperature of electrons and protons, their density and the ionization fraction. From such information it is also possible to seek for efficient Cosmic Ray production looking at missing energy of the thermal plasma which could have been converted in accelerated particles. I will present several cases of SNRs where efficient acceleration has been inferred. In particular I will present the Halpha spectroscopy of Tycho's SNR obtained with the GHaFas spectrometer on the William Hershel Telescope. Such spectrometer clearly shows the presence of multiple Halpha lines that can be interpreted as due to the presence of a CR precursor generated ahead of the shock.