Over the last few years, IEEE 802.16 has been established as one of the most promising solutions for broadband wireless metropolitan area networks. In 2007, the standard was included as one of the radio access technologies for IMT-2000. The forthcoming version of the standard, IEEE 802.16m, is currently under evaluation by ITU as a radio technology for IMT-Advanced. In this paper we present a historical overview of the standard and provide a detailed technical discussion of the most relevant features introduced in the 2009 release and in the upcoming IEEE 802.16m. In particular, the downlink control signaling of these two versions is investigated in detail, and the results of a numerical analysis are illustrated for comparison purposes.