Following an introduction to relevant length scales of biological systems, I’ll focus on the nanoscale world of proteins. Collagen is the fundamental structural protein in vertebrates and is widely used as biomaterial. In spite of its prevalence and mechanical importance in biology, the mechanics of its triple-helical structure are surprisingly controversial: its flexibility is unresolved, as is its response to stress. My research group has been investigating these properties through single-molecule experiments. To do so, we have developed imaging algorithms to use in atomic-force microscopy, described models for polymers with inherent curvature, and built a new instrument for high-throughput single-molecule force spectroscopy, the mini-radio centrifuge force microscope (MR.CFM).  I’ll describe what we have learned about collagen’s flexibility and stress response, why these properties are important, and how our work resolves some of the many contentious findings regarding collagen’s mechanics.