This chapter develops the material in Chapter 7 and applies it to the modelling of systems with repair strategies. Failure rate and unavailability (probability of failure on demand) formulae are developed for the variations of ‘M out of N’ redundancy and the effect of different repair strategies is taken into account. Common cause failure is introduced and the most up-to-date partial beta model developed, along with ‘M out of N’ modifiers. Fault tree analysis is dealt with in detail and some modelling pitfalls and problems explained. Event tree modelling is also introduced.