Understanding the processes that led to the reionization of the Universe is among the most challenging tasks of modern extra-galactic astronomy. The main responsible for this phenomenon are thought to be high redshift star-forming galaxies. However, it is very difficult to constrain their contribution and only few detections of Lyman Continuum (LyC) emitters have been reported so far. Following theoretical models, several so-called indirect indicators of LyC radiation have been proposed. In particular, LyC seems tightly related to the Lyα emission properties both from theoretical works and low redshift observational studies. Using these pre-selection criteria has indeed proved to be a powerful method to identify LyC leakers at low redshift but there is a lack of consistent studies that relates these indicators to the LyC emission at high redshifts. In this seminar I will present the results obtained during my PhD where I have exploited the large number of ultra-deep spectra from the VUDS (Vimos Ultra Deep Survey) and VANDELS (a deep VIMOS survey for the CANDELS CDFS and UDS fields) surveys to investigate the LyC and Lyα emission properties from star-forming galaxies at z~4 and their correlations with other galaxy parameters.