Characterizing the nature, physical properties, and epoch of formation of the sources responsible for cosmic reionisation is one of the latest challenges of modern cosmology. Extending the searches beyond z~6.5 and back to ages where the Universe re-ionised requires extremely deep observations in the near-IR bands. Until the construction of JWST and 20-40 meter class ground-based telescopes, gravitational lensing surveys offer the only possibility of spectroscopically verifying the presence of an abundant population of low-luminosity sources. I will present the results of several projects targetting lensing clusters, aimed at constraining the abundance of star-forming galaxies at z ~ 6-10 using lensing magnification to improve the search efficiency and subsequent spectroscopic studies. These surveys combine complementary approaches, from the traditional “dropout” technique, applied on ground based images obtained with ISAAC/VLT or high resolution ACS/NICMOS imaging of the central regions of the clusters, to a systematic search for low-luminosity Lyman-alpha emitters with Keck/NIRSPEC, in the regions of maximal magnification. In spite of the uncertainties inherent to the small areas explored by these surveys, we demonstrate the practicality, over the next few years, of providing a valuable glimpse at the nature of the z~10 Universe ahead of the commissioning of future large facilities such as the ELT and the JWST.
ICC (Durham),