Discovered more than 2 decades ago, high-Tc superconductors have consolidated a large fraction of the condensed matter community in the search for the mechanism leading to he transition temperatures as high as 160 K.  In this talk I will overview recent developments in the experimental studies of high-Tc cuprates focusing on the results obtained by means of infrared spectroscopy. The crucial advantage of this technique is that one can get insights into the key characteristics of the superconducting state through a variety of model independent sum rules.  Specifically, our group at UCSD has employed new analysis based on sum rules to examine the energy scales associated the superconducting condensate and with the so-called pseudogap state. We believe that the sum rule results may be instrumental in narrowing down the field of plausible microscopic scenarios of high-Tc superconductivity.