The mechanism of kinesin stepping along microtubules has been studied extensively. There is now general agreement that the two identical motor domains (also termed “heads”) in the kinesin dimer move in a hand-over-hand manner, with the trailing head passing its stationary partner head and then attaching to the next available binding site on the microtubule (Asbury et al., 2003, Kaseda et al., 2003 and Yildiz et al., 2004). The conformational change that drives this hand-over-hand motion has been proposed to be the “docking” of a ∼14 aa peptide (the “neck linker”) onto the catalytic core of the “front” head, which occurs upon binding of ATP (Rice et al., 1999). Since the C terminus of the docked neck linker is repositioned toward the microtubule plus end, this conformational change would be expected to shift the position of the “rear” head forward and bias its reattachment to the next available tubulin-binding site in the plus end direction. Although evidence for this conformational change has been obtained (Rosenfeld et al., 2001, Skiniotis et al., 2003 and Tomishige et al., 2006), it still remains controversial whether the neck linker docking powers kinesin movement (Schief and Howard, 2001, Block, 2007 and Carter and Cross, 2005).