Using the basic building blocks of collagens, elastins and proteoglycans, the human body is capable of manufacturing our large range of different structural tissues. Understanding how these structural components combine to create such widely varying tissues with diverse mechanical characteristics is a topic of interest for a range of research areas. However, probing the sub-structural mechanics to investigating these structure-function relationships is complex, as the series of hierarchical levels in connective tissues range in size from the Angstrom to millimeter level. Tendon has received considerable interest, as its simple aligned structure provides a promising route for investigating structure-function relationships. Tendon is an aligned, multi-level fibre composite structure, built predominantly from the collagen molecule to make a material with excellent tensile strength. The paper reviews the current state of research relating to tendon structure-function behaviour throughout the tendon hierarchy, building from the collagen molecule at the nano scale to the complete tendon.