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Beamforming is a powerful technique which has been widely used in signal processing, radar and sonar, biomedical, and particularly in communications, where the basic idea is to optimally process signals received over different antennas, or the signals which are to be transmitted over different paths by adjusting the signal amplitudes and phases to form a strong beam toward the direction of interest, and at the same time, to avoid receiving or creating interference. In the past decade, with booming research in cooperative relay communications, a new type of beamforming, namely network beamforming, has appeared and developed to fulfill the needs of the ever-evolving wireless systems. A network beamformer is implemented at neither the transmitter nor the receiver but at the intermediate relays to adaptively process signals and conduct the tasks of both the receive beamformer and the transmit beamformer. In this chapter, a systematic overview of various network beamforming approaches and solutions are presented for multi-relay cooperative networks with a wide variety of configurations, including one-way and two-way communications, single-user and multi-user cases, flat-fading and frequency-selective channel models, and networks with perfect and partial channel state information.