The crystal structure of a material plays an important role in determining its electronic properties. Changing from one crystal structure to another involves a phase transition which is usually controlled by a state variable such as temperature or pressure. In the case of trilayer graphene, there are two common stacking configurations (Bernal and rhombohedral) which exhibit very different electronic properties [1][2][3][4][5][6][7][8][9][10][11]. In graphene flakes with both stacking configurations, the region between them consists of a localized strain soliton where the carbon atoms of one graphene layer shift by the carbon-carbon bond distance [12][13][14][15][16][17][18]. Here we show the ability to move this strain soliton with a perpendicular electric field and hence control the stacking configuration of trilayer graphene with only an external voltage. Moreover, we find that the free energy difference between the two stacking configurations scales quadratically with electric field, and thus rhombohedral stacking is favored as the electric field increases. This ability to control the stacking order in graphene opens the way to novel devices which combine structural and electrical properties. * leroy@physics.arizona.edu 2 Multilayer graphene has attracted interest in large part due to the ability to induce a sizable band gap with the application of an electric field. The exact nature of the electronic properties of multilayer graphene is controlled both by the number of layers as well as their stacking configuration. The equilibrium in-plane crystal structure of graphene is hexagonal [19], and deviations from this equilibrium require a large amount of energy. Upon stacking multiple graphene sheets, Bernal-stacking -where the A-sublattice of one layer resides above the B-sublattice of the other layer -represents the lowest energy stacking configuration. Thus under normal circumstances, any two graphene layers in a graphite stack will be Bernal-stacked with respect to one another. However, when examining layers more than one apart, there can be multiple nearly-degenerate stacking configurations (2 (n−2) such configurations for n layers) [1]. For example, in the simplest case of trilayer graphene, the top layer may lie directly above the bottom layer (denoted Bernal-or ABA-stacked), or may instead be configured such that one sublattice of the top layer lies above the center of the hexagon of the bottom layer (denoted rhombohedrally-or ABC-stacked). Applying a perpendicular electric field breaks the sublattice symmetry differently depending on the stacking configuration, and thus is capable of re-ordering the energy hierarchy of the stacking configurations [1][2][3][4][5][6][7][8][9][10][11]. As a consequence, multilayer graphene exhibits the rare behavior of crystal structure modification, and hence modification of electronic properties, via the application of an external electric field.To examine this effect, we perform scanning tunneling topography (STM) and scanning tunneling spectroscopy (STS) measur...