In this lecture on Solid State Joining Processes, we discuss how joints are formed without melting, using controlled plastic deformation, diffusion, and recrystallization. The session covers advantages over fusion welding—such as reduced heat input, narrower HAZ, minimal defects, and suitability for heat-sensitive or dissimilar materials. Processes like friction welding, friction stir welding, ultrasonic welding, diffusion bonding, and roll bonding are introduced, along with the role of surface preparation, mechanical interlocking, and deformation scale in achieving strong metallurgical bonds.