Abstract: In this talk I will be presenting the results from our systematic survey to search for 21-cm absorption in an unbiased sample of strong MgII systems at intermediate redshifts. This survey has allowed us to constrain the number per unit redshift of 21-cm absorbers (n21) at $z\leq 1.5$. We show that n21 has fallen by a factor 4 from =0.5 to =1.3 and the decrease is most likely due to the evolution of cold neutral medium filling factor of the galaxies. Based on these results I will show that a blind search of 21-cm absorbers with ASKAP (made possible by its wide field of view and large instataneous bandwidth) will unearth a large number of 21-cm absorbers at $z\leq 1$. This ASKAP survey will allow us to measure the n21 without resorting to any preselection based on the UV absorption lines. This will be crucial for probing the thermal state of the interstellar medium of galaxies in the redshift range where most of the evolution in star-formation rate density takes place. This survey in combination with various follow-up observations can be used for (1) investigating the metallicity and dust content of the 21-cm absorbers, (2) studying the morphology of the absorbing gas and their connection with galaxies, (3) the searches of molecules and (4) probing the time evolution of various fundamental constants.