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This thesis is concerned with the iron loss models for electrical machines, focussing on permanent magnet (PM) electrical machines. Four common conditions for investigation of iron losses in PM electrical machines are considered, i.e. sinusoidal flux density, flux density with DC bias, flux density distortion and arbitrary flux density. In particular, the temperature effects on the iron loss are systematically investigated and modelled under each condition. Four of the most commonly used iron loss models for sinusoidal flux density are initially introduced and the most accurate iron loss model is identified by utilising a steel lamination ring specimen test procedure. The temperature effect on the iron loss is then investigated. It is found that the existing iron loss models without temperature consideration will be inaccurate when the temperature varies. Therefore, an improved iron loss model considering temperature influence is developed. For the influence of DC bias flux density, the combined influence of DC bias flux density and temperature is experimentally confirmed by a modified steel lamination ring specimen test procedure. An improved iron loss model is then proposed for the flux density with DC bias while considering the influence of temperature. For the influence of flux density distortion, an improved iron loss model for considering the flux density distortion and temperature influence is also presented in this thesis. In order to validate the effectiveness of improved models in electrical machines, iron loss tests are carried out on an interior PM (IPM) machine. The IPM machine is heated to different temperatures to evaluate the iron loss models for considering the temperature influence. Furthermore, in order to validate the improved model for DC bias flux density, ferrite magnets are installed into the rotor to generate DC bias flux density in the machine. Moreover, iron loss tests on the machine when fed by a pulse width modulation (PWM) inverter are carried out to evaluate the improved iron loss model for the influence of flux density distortion. Finally, based on the above investigations on all the influential factors of iron loss, an iron loss model for arbitrary flux density accounting for the temperature influence is developed. The iron loss model is validated by iron loss tests on a variable flux reluctance machine.