The paper reports on experiments demonstrating that charge current flowing in-plane in a thin film of the topological insulator Bi$_2$Se$_3$ at room temperature can generate a strong spin-transfer torque on an adjacent ferromagnetic permalloy (Py = Ni$_{81}$Fe$_{19}$) thin film. The torque is consistent with the expected direction from the topological surface state of Bi$_2$Se$_3$. The strength of the torque per unit charge current density in Bi$_2$Se$_3$ is found to be greater than for any other spin-torque source material measured to date, even for non-ideal TI films. The findings suggest that topological insulators have the potential to enable efficient electrical manipulation of magnetic materials at room temperature for memory and logic applications. The study uses spin-torque ferromagnetic resonance (ST-FMR) techniques to measure the torque and theoretical modeling to interpret the results. The results indicate that the spin torque angle for Bi$_2$Se$_3$ at room temperature is larger than for any previously-measured spin-current source material, and that the majority of the current flows through the metallic magnet, which is not ideal for practical applications. However, the findings suggest a new strategy for implementing low-power nonvolatile magnetic memory and logic structures using TIs as room-temperature sources of spin torque coupled to insulating magnetic layers.The paper reports on experiments demonstrating that charge current flowing in-plane in a thin film of the topological insulator Bi$_2$Se$_3$ at room temperature can generate a strong spin-transfer torque on an adjacent ferromagnetic permalloy (Py = Ni$_{81}$Fe$_{19}$) thin film. The torque is consistent with the expected direction from the topological surface state of Bi$_2$Se$_3$. The strength of the torque per unit charge current density in Bi$_2$Se$_3$ is found to be greater than for any other spin-torque source material measured to date, even for non-ideal TI films. The findings suggest that topological insulators have the potential to enable efficient electrical manipulation of magnetic materials at room temperature for memory and logic applications. The study uses spin-torque ferromagnetic resonance (ST-FMR) techniques to measure the torque and theoretical modeling to interpret the results. The results indicate that the spin torque angle for Bi$_2$Se$_3$ at room temperature is larger than for any previously-measured spin-current source material, and that the majority of the current flows through the metallic magnet, which is not ideal for practical applications. However, the findings suggest a new strategy for implementing low-power nonvolatile magnetic memory and logic structures using TIs as room-temperature sources of spin torque coupled to insulating magnetic layers.