This book presents an integrated study of metamaterial-based large-scale antenna arrays and beamforming optimization for both Half-Duplex (HD) and Full-Duplex (FD) massive MIMO (mMIMO) systems. As a cornerstone of future wireless communications, mMIMO provides substantial improvements in capacity and spectral efficiency, which this book illustrates. With strategically designed beamforming, these arrays can precisely direct energy toward intended users, while effectively suppressing interference. Metamaterial structures with tunable electromagnetic properties further enhance performance by enabling compact, high-isolation antenna elements and novel interference mitigation strategies. In addition, hybrid beamforming architectures are investigated to achieve an optimal balance between system performance and hardware complexity.