The magnetic nozzle (MN) is an appealing plasma acceleration technology that enables the electrodeless, contactless, and adaptable control of a plasma jet. Using a 2-D, two-fluid plasma model, the core physical principles that enable the operation of a propulsive MN are reviewed, including the key mechanisms involved in thrust generation, plasma acceleration, and plasma detachment. Simulations indicate the parametric regimes that maximize the propulsive performance of the device. Extensions of the model are used to explore additional physical effects and their influence on the plasma expansion. While there are open questions to address, MNs appear to be a promising candidate for high-efficiency, high-durability plasma propulsion in future space missions.