The present invention relates to a combustion controller for controlling the combustion of a flow of combustible and/or combusting fluid. The combustion controller comprises an inlet and an outlet which defines a flow path between them. A magnetic-field generator is arranged to generate a magnetic field across the flow path such that in use the fluid flows in the flow path through the magnetic field. As the fluid flows through the magnetic field an electric current is induced in the fluid. This results in energy being supplied to the fluid. This energy can assist is reignition. If the magnetic field is an alternating magnetic field then this induces an alternating current in the fluid. The frequency of this current can be controlled such that certain chemical reactions are either promoted or inhibited.