The armed forces ability to constitute a threshold against possible attacks has been highlighted in the Swedish defense policy debate. The purpose of this study is to give additional perspectives on a Swedish threshold to deter military attacks, by developing some practical and theoretical points for action and thinking. A threshold can be seen as a limited form of deterrence. Deterrence involves three components that work together: (1) a credible will to respond to an armed attack; (2) a credible capability to respond to an armed attack, and (3) a credible communication of the will and capability to respond to an armed attack. A threshold effect represents the impact the defender has on the aggressor before he decides to initiate an armed aggression. A threshold is sufficient when the aggressor refrains from an attack or feels compelled to increase his effort to implement or continue the attack. The focus is on the aggressor's view of the outcome in relation to the possible costs of an attack, and is thus based on perceptions. A threshold capability includes the capacities the defender disposes which an aggressor weighs in his calculus when considering an attack on the defender. A threshold capability must be linked to real circumstances to be credible. The report discusses the threshold against armed aggressions on Sweden based on the ability to harm the attack, i.e. deterrence by denial, and the ability to harm the attacker, i.e. deterrence by punishment. The report argues that the ability to credibly damage the aggressor provides a deterrent effect and that Sweden should seek to obtain deterrence mechanisms that can link together Swedish security with the safety of others.