  It has been several years since the first detection of Gunn-Peterson troughs
in the z > 6 Ly-alpha forest and since the first measurement of the Thomson
scattering optical depth through reionization from the cosmic microwave
background (CMB). Present day CMB measurements provide a significant constraint
on the mean redshift of reionization, and the Ly-alpha forest provides a lower
bound on the redshift at which reionization ended. However, no observation has
provided definitive information on the duration and morphology of this process.
This article is intended as a short review on the most promising observational
methods that aim to detect and study this cosmic phase transition, focusing on
CMB anisotropies, gamma ray burst afterglows, Ly-alpha emitting galaxies, and
redshifted 21cm emission.
