The interaction of radiation from distant sources with the intervening medium is an invaluable way to map the distribution and chemical composition of matter in the high-redshift universe. During the past 50 years, however, optically-thick clouds that give rise to Lyman limit systems (LLSs) have received much less attention than the Lyman-alpha forest or the damped Lyman-alpha absorbers (DLAs). Thus, the connection between these absorbers and galaxies still remains for most part elusive. The growing interest in studies of the circumgalactic medium is, however, putting the spotlight on the link between LLSs and galaxies. In this talk, I will present results from ongoing work to constrain the physical properties of LLSs, and I will discuss ways to exploit these absorbers, together with DLAs, as tools for the study of the halo gas and star formation in the high redshift universe.