This chapter addresses one of the lord lieutenancies’ most important roles, the organisation and running of the county militias intended to defend against invasion attempts. The chapter firstly looks at the militia chronologically. It considers early Elizabethan attempts to reform the militia, notably the creation of the ‘Trained Bands’ in the years leading up to the crisis of the Spanish Armada (1588). It then looks at the crisis itself, during which the militia did not have to fight, but demonstrated good levels of organisation and readiness, and finally looks at how readiness was maintained during the remaining 15 years of war, when there were several further invasion scares. The second part of the chapter assesses the militia thematically: its organisation, training and equipment. Overall, the chapter concludes that the militia, although inconsistent and often badly run, made real improvements over the period in terms of weaponry, organisation and training. Whilst the military prowess of the militia remained untested, the chapter shows that the ability of the privy council to generate activity and the willingness of the lieutenancies and the wider population to carry it out was greater than usually thought.