Cosmic reionization marks the latest phase transition of the IGM in the early Universe. High-redshift (redshift around 6 or higher) quasars and galaxies are powerful tools to probe this epoch. I will review how the absorption spectra of quasars and the statistical properties of galaxies (particularly Lyman-alpha emitting galaxies) are used to estimate the IGM state during the reionization epoch. Then I will explain the important energy source problem, i.e., what astrophysical sources provided ionizing photons for reionization. In the end I will briefly mention what future facilities may help us better understand the reionization.