Various aspects of the present invention relates to the control and manipulation of fluidic species, for example, in microfluidic systems. In one aspect, the invention relates to systems and methods for making droplets of fluid surrounded by a liquid, using, for example, electric fields, mechanical alterations, the addition of an intervening fluid, etc. The invention also relates to systems and methods for fusing droplets according to another aspect of the invention, for example, through charge and/or dipole interactions. In some cases, the fusion of the droplets may initiate or determine a reaction. In still another aspect, the invention relates to systems and methods for sorting droplets, e.g., by causing droplets to move to certain regions within a fluidic system. Examples include using electrical interactions (e.g., charges, dipoles, etc.) or mechanical systems (e.g., fluid displacement) to sort the droplets.