Chemotactic movement of ionic liquid droplets Herein we report the chemotactic behaviour of self-propelled droplets composed solely of the ionic liquid (IL) trihexyl(tetradecyl)phosphonium chloride ([P6,6,6,14][Cl]). These droplets move spontaneously across the liquid/interface and are guided to specific destinations within open fluidic channels through the use of chloride gradients. The movement of these droplets is controlled by the triggered release of the [P6,6,6,14] + cation, a component of the IL and a very efficient cationic surfactant. Surfactant release has been previously used to develop smart droplets which can solve complex mazes [1] or can be photo-manipulated [2]. In this study the [P6,6,6,14]+ diffuses from the droplet into the aqueous solution which causes a local drop in surface tension, this creates marangoni like flows which drive the droplet from areas of low surface tension to high surface tension. The rate of [P6,6,6,14]+ release depends on the concentration of the chloride in the aqueous solution, as the formation of free [P6,6,6,14]+ (the active surfactant at the air-aqueous interface) through dissociation of the relatively closely associated [P6,6,6,14][Cl] ions in the IL depends on the local Cl- concentration at the IL-aqueous boundary. We envision that these smart IL droplets could be used for a variety of applications within the microfluidic sector such as dynamic sensing, cargo transport and serve as micro-vessels for chemical reactions. Furthermore we believe this new approach to micro-vehicle movement will provide a much broader base for the development of a wide range of new droplet chemistries that exploit the vast and still rapidly growing numbers of ionic liquids. [1] I. Lagzi, S. Soh, P. Wesson, K. Browne and B. Grzybowski, Journal of the American Chemical Society, 2010, 132, 1198-1199. [2] L. Florea, K. Wagner, P. Wagner, G. G. Wallace, F. Benito‐Lopez, D. L. Officer and D. Diamond, Advanced materials, 2014.