In recent decades, significant progress has been made in enhancing the performances of additively manufactured metal components. Advancements in strengthening technologies have played a crucial role. Among these, in-situ strengthening strategies, such as in-situ alloying, in-process heat treatment, in-situ precipitation and hybrid multiprocessing, offer unique advantages in enhancing processability and tailoring microstructure and mechanical performances in a cost-effective manner. These methods have led to improvements in defect mitigation, microstructure and bonding strength between adjacent layers, which resulted in improved mechanical performances of the manufactured functional metal components. This special issue comprehensively addresses various aspects of in-situ strengthening strategies for manufacturing high-performance metal components. The topics include but are not limited to novel concepts, new materials, specific mechanisms, innovative design, and in-depth characterizations. This special issue aims to provide a guide for the in-situ strengthening of additive manufacturing.