HETDEX (Hobby-Eberly Telescope Dark Energy eXperiment) is a galaxy survey targeting Lyman-alpha emitters (LAEs) at high redshifts (1.9<z<3.5). Starting from Spring 2015, HETDEX will observe about a million LAEs over ~400 sq. degrees, which corresponds to ~10Gpc^3 in volume. In this talk, I will summarize the survey design, observing strategy, as well as the science goal of the survey.