Chapter 3 showed how the multipath channel causes significant impairments to the signal quality in mobile radio communication systems. As signals travel between the transmitter and receiver, they get reflected, scattered, diffracted, and shadowed. In addition, user s mobility gives rise to Doppler shift in the carrier frequency. As a result, those signals experience fading because of the attenuation and phase shifts when they are combined at the receiver. Another source that degrades the performance of signal reception in a mobile environment is interference, especially in interference-limited systems such as those based on CDMA. Techniques that overcome these impairments and improve system performance are examined in this chapter, namely, diversity and adaptive beamforming, both of which are spatial techniques. Diversity techniques provide a diversity gain or a reduction in the margin required to overcome fading. In a digital communication system, this results in an improvement in the required SNR or E _b /N _o necessary to achieve a given quality of service in terms of bit error rate (BER) or FER. Similarly, beamforming provides several types of improvements in terms of array gain, interference reduction, and spatial filtering, which have the cumulative effects of improving E _b /N _o as well. We will show how these techniques are applied on both the uplink and downlink and discuss the limitations of each approach.