Incipient plasticity refers to the onset of plastic deformation and plays a pivotal role in understanding the strength and failure mechanism of certain materials. It helps predict how materials respond under mechanical stress at the atomic scale. This chapter summarizes the key concepts underlying incipient plasticity, including classical yield criteria, experimental characterization techniques, and the methods for initiating the plastic deformation. Specifically, nanoindentation and molecular dynamics simulations have been thoroughly discussed as powerful tools to probe early-stage plasticity. The chapter also critically examines existing literature and highlights the central role of dislocations nucleation in governing incipient plasticity. Furthermore, a discussion on how microstructural defects (such as grain boundaries, stacking faults, and interfaces) affect dislocation behavior and deformation onset is provided. These insights reveal fundamental mechanisms of deformation initiation and enable the design of stronger and more reliable materials.