Millimeter–wave (mmWave) communications have been regarded as a key technology for the next–generation cellular systems since the huge available bandwidth can potentially provide the rates of multiple gigabits per second. Conventional precoding and combining techniques are impractical at mmWave scenarios due to manufacturing cost and power consumption. Hybrid alternatives have been considered as a promising technology to provide a compromise between hardware complexity and system performance. A large number of hybrid precoder designs have been proposed with different approaches. One possible approach is to search for minimizing the Euclidean distance between hybrid precoder and the full-digital precoder. However, this approach makes the hybrid precoder design becomes a matrix factorization problem difficult to deal due to the hardware constraints of analog components. This doctoral thesis proposes some hybrid precoder and combiners designs through a hierarchical strategy. The hybrid precoding/combining problem is divided into analog and digital parts. First, the analog precoder/combiner is designed. Then, with the analog precoder/combiner fixed, the digital precoder/ combiner is computed to improve the system performance. Furthermore, linear and no-linear optimization methods are employed to design the analog part of the precoder/combiner. The viability of these proposals is evaluated using different data detection techniques and analyzing the system performance in terms of bit error rate (BER), sum rate, and other metrics, in indoor mmWave scenarios considering massive MU-MIMO downlink. Also, this work proposes a method to find fairly tight analytic approximations to the obtained BER performance. The methodology proposed would require the knowledge of the probability density function (pdf) of the variables involved, which are unknown for mmWave scenarios. In order to solve this problem, Gamma pdf approximations are used. The analytic BER approximations resulted in differences no larger than 0.5 dB with respect to the simulation results in high SNR.