Mechanics of Biological Systems and Materials & Micro-and Nanomechanics, Volume 4 of the Proceedings of the 2019 SEM Annual Conference & Exposition on Experimental and Applied Mechanics, the fourth volume of six from the Conference, brings together contributions to important areas of research and engineering. The collection presents early findings and case studies on a wide range of topics, including: Extreme NanomechanicsIn-Situ Nanomechanics Expanding Boundaries in Metrology Micro and Nanoscale Deformation MEMS for Actuation, Sensing and Characterization 1D & 2D Materials Cardiac Mechanics Cell Mechanics Biofilms and Microbe Mechanics Traumatic Brain Injury Orthopedic Biomechanics Ligaments and Soft Materials