Well tools utilizing swellable materials. Actuators for well tools may incorporate swellable materials as force generating devices. A well tool includes an actuator which actuates the well tool in response to contact between a swellable material and a well fluid. A method of actuating a well tool includes the steps of: installing a well tool including an actuator; contacting a swellable material of the actuator with a well fluid; and actuating the well tool in response to the contacting step. A well system includes a well tool with a flow control device and a swellable material. The well tool is operative to control flow through a passage of a tubular string in response to contact between the swellable material and well fluid.