The energy loss from the neutron star -- as inferred from the secular increase in rotation period -- is much greater than that emitted in either the radio or the other observed wavelengths. A primary motivation of magnetospheric theory is to trace the mode in which this energy and the associated angular momentum are in fact carried off from active pulsars. This review concentrates on the special case in which the magnetic and rotation axes are aligned. Electrons emitted from the polar caps are accelerated to highly relativistic energies by the electric force and simultaneously pick up angular momentum from the magnetic torque. Some process of angular momentum dissipation occurring beyond the light-cylinder is then required, both to yield the continuous spin-down of the star, and also to allow the electrons to cross magnetic field lines and so complete their circuits back to the star. Within the framework of classical physics, this could occur if most of the spin-down energy is lost through incoherent photon emission in an equatorial domain beyond the light-cylinder, but this would generate $\gamma $-radiation far in excess of that observed. Transport away of the angular momentum via a relativistic wind requires the generation of a quasi-neutral plasma. Gamma-rays emitted by outflowing electrons will produce electron--positron pairs in the strong magnetic field near the star, and highly energetic electrons returning to the star may also generate a mixed plasma by pair production or by surface spallation. Coupling with the circulating primary electron current may then ensure that the dominant angular momentum loss is via the wind rather than through photon emission.