In situ nanomechanics is an emerging field that investigates the mechanical properties and deformation mechanisms of nanostructured materials. The in situ nanomechanics research is typically conducted by integrating the real-time mechanical testing inside an electron microscope and the mechanics modeling with atomic resolution. It provides a powerful approach to visualize the intrinsic nanomechanical behavior of materials. In this talk, I will present the recent in situ nanomechanics studies in my group, including deformation twinning in BCC nanocrystals (Nature Materials, 14, 594, 2015); and stress-induced amorphization in silicon nanocrystals (Nature Nanotechnology, 11, 866, 2016). I will also present our ongoing work on the nanomechanics of heterogeneous nanostructured high-entropy alloys and 3D-printed steel. The in situ nanomechanics studies provide new insights that cannot be offered by traditional mechanics approaches. Ultimately, the in situ nanomechanics research aims to enable the design of nanostructured materials to realize their latent mechanical strength to the full.