This course provides students with a comprehensive understanding of the fundamental concepts that govern the behaviour of metals under mechanical stress. Through a structured curriculum, this course examines the behaviour of crystalline defects, especially dislocations, and the strategies employed to enhance mechanical properties. Students engage in lectures where they unravel the theoretical foundations underlying dislocation behaviour and strengthening mechanisms. These sessions serve as a platform for in-depth exploration, as students grasp the significance of dislocations in materials' plastic deformation, their role in influencing mechanical strength and their application in alloy design. The course extensively covers dislocation theory, as well as strengthening mechanisms, including work-hardening, solid solution strengthening, precipitation hardening and grain boundary effects. In addition, through participating in interactive online tutorials, students are provided with the opportunity to practise their problem solving skills, apply their theoretical knowledge in the context of real-world scenarios, deepen their comprehension of the subject matter and receive feedback on their learning. By the end of the course, students should have a profound appreciation of how dislocation theory intertwines with strengthening mechanisms to dictate and allow control over the mechanical properties of materials. This knowledge will equip students to analyse and design materials with improved mechanical performance for real-world applications in industries ranging from aerospace to advanced manufacturing.