I am involved in different projects searching for the earliest galaxies formed during, or shorlty after, the cosmic reionization epoch. Characterizing the nature, physical properties, and epoch of formation of these sources, probably responsible for reionizing the intergalactic medium, 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.