This book focuses on the functionality and the enhancement of MAC Layer on WiMAX broadband wireless system. The WiMAX technology is mostly referred to IEEE802.16-2004 and IEEE802.16-2005 with some requirements taken from IEEE802.16j-2006 D2 and initial documents of IEEE802.16m. The first part of this book presents an evaluation of the overhead on the MAC management messages of IEEE 802.16. It is followed by the improvement mechanism of MAC functionality. The final part discusses about the enhancement of handover strategy for advance air interface system.