Motion is fundamental to life. Everyone is familiar with the macroscopic motion of muscle contraction. There are also exquisite, essential motions taking place at the level of cells and molecules. The cells in our immune system crawl around our bodies and engulf invading bacteria. Cilia in our lungs beat to remove inhaled debris. Vesicles are transported across neurons in our brains, spinal chords, and limbs. In all cases, the motion is generated by tiny protein machines, the molecular motors. Work in my lab aims to understand how these protein machines convert chemical energy into mechanical work, by studying the motions and forces produced by purified motors and organelles. State-of-the-art optical trapping techniques are used to manipulate the motors, to apply force to them, and to measure the nanometer-scale motions they generate. A variety of tools from molecular biology and biochemistry are also used, to purify the proteins and organelles, and to modify the proteins in specific ways.