Abstract: Aluminum/steel hybrid structures, leveraging the synergistic advantages of aluminum alloys and steel, have emerged as a critical solution to lightweighting demands in industries such as automotive manufacturing and aerospace engineering. However, the significant differences in thermophysical and chemical properties between aluminum and steel pose inherent challenges for conventional fusion welding, which seriously restricts the joint quality and large-scale industrial application of aluminum/steel components. Solid-state friction welding, characterized by core advantages including no liquid phase formation, low heat input, and the ability to break up interfacial oxide films, effectively circumvents the inherent limitations of fusion welding, thus establishing itself as a pivotal technical route for aluminum/steel dissimilar interface formation. To date, three mature technological variants have been developed—traditional friction welding, friction stir welding, and friction stir additive manufacturing—which achieve a balance between interfacial bonding quality through the “low heat input and severe plastic deformation” mechanism. However, current research still faces some problems, such as the limited capability for joining thick-section components, insufficient precision in intermetallic compound layers regulation, and inadequate investigations into adaptability under extreme environments. These limitations hinder further technological breakthroughs. Thus, this review systematically summarizes the mainstream technical types, process characteristics, and application scenarios of aluminum/steel solid-state friction welding from the perspectives of technical methodology and mechanism exploration. Simultaneously, it conducts an in-depth analysis of the core mechanisms underlying interfacial mechanical bonding and metallurgical bonding, and further explores cross-scale regulation strategies. This work aims to provide research insights for the subsequent optimization of aluminum/steel solid-state welding technologies, the deepening of bonding mechanism understanding, and the direction of industrial application.