紧急状态是指一个国家陷入或即将陷入危机，有可能会影响国家的发展及存亡，由国家元首使出超过平常法治范围的特别措施。现在多数先进国家会将权力下放至国会，让国会通过实施紧急状态，再由国家元首宣布全国进入紧急状态。根据危机程度的不同，所采取的紧急状态的办法也不同。

所谓的危机的代表如外国武力攻击、内战、暴动、恐怖攻击、大规模灾害等，近些年来因为禽流感和爱滋病等疾病以及暴雪、低温等恶劣气候而发布紧急状态的例子也开始增多。

紧急状态时所采行的措施主要包含动员国家的公务员（包含警察及军队）、征收派发国家的公共物品、发布政令、检查讯问和搜索民宅等行为。碰到内战时，会特别限制集会自由和组党结盟等限制市民权利的措施，因此紧急状态和戒严的性质其实相当接近。

A government or division of government (i.e. on a municipal, provincial/state level) may declare that their area is in a state of emergency. This means that the government can suspend and/or change some functions of the executive, the legislative and/or the judiciary during this period of time. It alerts citizens to change their normal behavior and orders government agencies to implement emergency plans. A government can declare a state of emergency during a time of natural or human-made disaster, during a period of civil unrest, or following a declaration of war or situation of international/internal armed conflict. Justitium is its equivalent in Roman law, where Senate could put forward senatus consultum ultimum.