Tearing modes often limit the performance of tokamak plasmas, because the magnetic islands which they generate lead to a loss of confinement, or even a disruption. A particularly dangerous instability is the neoclassical tearing mode, which can grow to a large amplitude because of the amplification effect that the bootstrap current has on an initial `seed' magnetic island. This paper will address the mechanisms which dominate the neoclassical tearing mode evolution, and thereby identify possible control techniques.