Lyman alpha line is the strongest line originating in star forming regions, and the Lya photons, that at rest have a wavelength in the far UV, are redshifted in the optical window at z>2. Therefore, Lyman alpha is routinely used to explore the high redshift Universe, up to and even beyond the epoch of reionization. However, the line is resonant, meaning that it is easily scattered/absorbed in the IGM of galaxies. As a result, “Lya escape fraction” (the fraction of the produced Lya photons that can eventually escape from the galaxy) is a complicated function of star formation activity, IGM geometry, kinematics and ionization state. I will review the techniques that are used to identify high redshift Lya emitters, to constrain their luminosity function and to understand their properties. I will present the results that I obtained studying galaxies with and without Lya emission in the Vimos-VLT Deep Survey (VVDS) and the Vimos-VLT Ultradeep Survey (VUDS), two of the biggest spectroscopic campaigns ever undertaken at the VLT.