The actions of the interossei and lumbricals are many and their loss causes significant impairment of hand function. Many procedures have been described to restore intrinsic function following ulnar nerve palsy. There are many biomechanical issues involved in tendon transfers, including choice of muscle-tendon unit, route, insertion site, tension and drag. The surgeon, therefore, should have a good understanding of biomechanical principles to ensure optimal results. In this article the principles of biomechanics are reviewed with specific reference to tendon transfers for intrinsic reconstruction in ulnar palsy, along with their practical implications.