5G systems will enable important and challenging communication scenarios, namely enhanced mobile broadband, massive machine type communications for the Internet of Things, ultra-reliable and low latency communications for real-time and safety critical applications and support for high density of mobile users. These types of communication will require considerable improvements and breakthroughs in terms of data rate, network capacity, connection density, end-to-end latency, spectral efficiency, power consumption, mobility, coverage and cost. Some key technologies that are being evaluated for these purposes include massive MIMO, 3D beamforming, ultra-dense networks, new physical layer waveforms and channel access mechanisms (e.g. full-duplex techniques), usage of millimeter waves spectrum bands and new paradigms in the core and access network architectures (e.g. Cloud Radio Access Network approaches). This Special Section is devoted to the presentation and discussion of advanced signal processing algorithms and novel implementation architectures that will support the development of 5G wireless communications systems.