The Lyman-alpha emission line has proven to be quite powerful at detecting high redshift star-forming galaxies (~ 3<z<7). Being supposedly the building blocks of nowadays galaxies, the study of these so-called Lyman-alpha Emitters (LAE) is important to understand their role in the hierarchical scenario of galaxy formation. Observational and theoretical arguments suggest that both complex Lyman-alpha radiative transfer and gas outflows play a major role in shaping the observed Lyman-alpha properties of high redshift galaxies. With these assumptions in mind, I will present an original model for LAEs in the cosmological context based on the GALICS semi-analytic model of galaxy formation. Interestingly, the model predicts that most of Lyman-alpha photons are able to escape from low-mass galaxies, suggesting that Lyman-alpha fluxes can be used to trace the Star Formation Rate for those objects. Conversely, the Lyman-alpha escape fraction is strongly dispersed for massive galaxies, depending on their physical properties. I will show that the model can reproduce most of the observational constraints (i.e. Lyman-alpha and UV luminosity functions, stellar masses, clustering, etc.) of LAEs, and will investigate their link with the UV-selected high redshift galaxy population (i.e. Lyman-Break galaxies). Despite the simplifying assumptions it is based on, this model seems thus able to catch important effects governing Lyman-alpha emitting galaxies. The model can furthermore be used as a predictive tool in the context of forthcoming instruments, aiming at probing high redshift Lyman-alpha galaxies.