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Even though WiMAX technology offers high data rates, the overall capacity over the air is shared among several WiMAX users. This is especially true for the WiMAX support of femto cells. In this scenario very small wireless cells, covered by short-range technologies such as WLAN or Bluetooth, are wirelessly connected to the Internet backbone by WiMAX links. The number of accumulated users will be high and any means to gain additional capacity are more than welcomed. An effective approach to increase capacity is to utilize header compression. In the wireless world, Robust Header Compression (ROHC), as standardized in RFC3095 (Bormann et al., 2001), is a widely applied header compression scheme. ROHC is a method to reduce the overhead of the packet header information down to 10% or less. This method is especially effective if the payload is relatively small in contrast to the header itself. In this chapter we will motivate the use of ROHC in WiMAX, as proposed in the WiMAX documents (Fitzek et al., 2004), and demonstrate the potential gain of using ROHC for WiMAX femto cells by implementation and measurements. The results presented here are the outcome of a collaborative work of acticom (acticom GmbH , 2008b) and VTT implementing acticom’s ROHC protocol stack in a commercial WiMAX system. As shown throughout this chapter, ROHC demonstrates outstanding performance over the standard system.