Many of the current and future Internet and digital multimedia applications such as Internet TV, streaming media, and localized services rely on the concept of mass content distribution. Wireless multicasting enable this in an efficient way, since it allows the provision of data and services to a group of users simultaneously using the same frequency band. In this context, wireless multicasting has emerged as a key technology for the next generation cellular and indoor/outdoor wireless networks. Several techniques have been proposed to enhance the spectral efficiency of the wireless multicast network while meeting the quality of service requirements of the network users. One of the most promising techniques is transmit beamforming, since it allows the exploitation of space as a resource at the transmitter in addition to the conventional resources such as time and frequency. In this thesis, we develop computationally efficient techniques to solve the beamforming problem for single-group and multi-group multicast networks. Our proposed techniques offer improved trade-off between performance in terms of transmitted power and computational complexity. First, the beamforming problem for single-group multicasting is considered, where all users receive the same datastream. The design approach is based on power minimization subject to individual signal-to-noise-ratio constraints at each user. We propose a channel orthogonalization and local refinement technique to efficiently solve this problem in an approximate way. The proposed techniques are shown to offer an attractive performance-to-complexity tradeoff as compared to state-of-the-art multiple-antenna multicasting algorithms. Next, we consider the beamforming problem for multi-group multicasting, where different datastreams are sent to multiple groups of users. A new approach is proposed to solve the power minimization problem using hierarchical modulation. The proposed approach enjoys a significantly reduced computational complexity and achieves a better performance in terms of the total transmitted power compared to the conventional approaches. Then, a non trivial extension of the channel orthogonalization-based approach, which was developed to approximately solve the beamforming problem for conventional single-group multicasting is proposed to the beamforming problem in singlegroup multicasting in cooperative relay networks. Similarly as in the previous network, the proposed technique has a small computational complexity and achieves a better performance in terms of transmitted power compared to other existing techniques. Finally, we propose a solution to the relay synchronization problem in cooperative relay networks with large delay spread. The proposed approach uses orthogonal frequency division multiplexing techniques to eliminate the effects of inter-symbol interference at the destination without applying artificial delays at the relays. In this approach, the additional traffic requirements of a fully synchronized relay network is completely avoided. The performance of the proposed scheme in terms of transmitted power is then compared to the performance of a fully synchronized relay network.