This presentation will address the growing interest in, and challenges with, Human-Machine Teaming (HMT). HMT promises adaptability, flexibility, and superior performance in military operations when humans are teamed with machine teammates. The scoping of HMT is broad; from simple human-computer or human-robot interaction to more complex 'human autonomy teaming' or 'manned unmanned teaming' (MUM-T). To better clarify, shape and influence the debate and pursuit of HMT going forward, I suggest we identify clear definitions and boundaries for discussion, policy guidance, and technical challenges. This will enable us to identify the existing technical and non-technical challenges or gaps, and provide meaningful guidance to the wide variety of stakeholders, such as operational commanders, acquisitions experts, technical leads, and policy makers.