The 3rd ACM Workshop on Millimeter-Wave Wireless Networks and Sensing Systems (mmNets'19) is focused on the design and implementation of new millimeter-wave (mmWave) protocols and systems that can enable multi-Gbps wireless connectivity for 5G-and-beyond cellular systems and wireless LANs, as well as new wireless sensing and imaging systems. The goal of the mmNets'19 workshop is to bring together researchers from mmWave hardware, communication and signal processing, wireless networking, and mobile applications to set the future research agenda of mmWave systems, and present innovative ideas that will help realize the vision of extremely high data rate wireless networks and novel advanced sensing applications. The workshop will serve as a platform for both academia and industry to identify key challenges, present solutions and advance the field of mmWave technology.