Abstract: Agility is regarded as important by many modern Defence forces, but the concept of agility is defined in many different ways. Flexibility, speed, and adaptability are some of the characteristics often associated with agility. In this paper, we outline a taxonomy which distinguishes six kinds of agility: tactical/operational agility, organisational agility, deployment agility, sustainment agility, acquisition agility, and conceptual agility. We describe some candidate metrics for the first two kinds of agility, and provide a number of examples illustrating them. These metrics can be used as a starting-point for dialogue on trade-offs between the different kinds of agility.