As robots that share working and living environments with humans proliferate, human-robot teamwork (HRT) is becoming more relevant every day. By necessity, these HRT dynamics develop over time, as HRT can hardly happen only in the moment. What theories, algorithms, tools, computational models and design methodologies enable effective and safe longitudinal human-robot teaming? To address this question, we propose a half-day workshop on longitudinal human-robot teaming. This workshop seeks to bring together researchers from a wide array of disciplines with the focus of enabling humans and robots to better work together in real-life settings and over long-term. Sessions will consist of a mix of plenary talks by invited speakers and contributed papers/posters, and will encourage discussion and exchange of ideas amongst participants by having breakout groups and a panel discussion.