Additive manufacturing (AM), also called 3D printing, has rapidly developed within the past four decades due to the availability and ease of using 3D printers. It has also been in high demand and of great importance in the aerospace, chemical, and medical industries. The manufacturing process has adopted several approaches to creating layer by layer building of components from computer models. AM process has been categorized into fusion-based and solid-state-based. The fusion-based processes have had their shortcomings with the complexities of the multiphysics involved in heating and cooling and the massive equipment cost. However, the solid-state AM processes have been proved to suppress the challenges the fusion-based AM has encountered. Therefore, this chapter examines some solid-state AM processes, such as additive friction stir AM, ultrasonic-assisted AM technique, and cold-sprayed AM, in the context of its microstructure, mechanical properties, challenges, and future trends.