Eschatology is a part of theology concerned with what are believed to be the final events of history, or the ultimate destiny of humanity. This concept is commonly referred to as the "end of the world" or "end time".

The word arises from the Greek ἔσχατος/ἐσχάτη/ἔσχατον, eschatos/eschatē/eschaton meaning "last" and -logy meaning "the study of", first used in English around 1550. The Oxford English Dictionary defines eschatology as "The department of theological science concerned with ‘the four last things: death, judgment, heaven and hell’."In the context of mysticism, the phrase refers metaphorically to the end of ordinary reality and reunion with the Divine. In many religions it is taught as an existing future event prophesied in sacred texts or folklore. More broadly, eschatology may encompass related concepts such as the Messiah or Messianic Age, the end time, and the end of days.

History is often divided into "ages" (Gk. aeons), which are time periods each with certain commonalities. One age comes to an end and a new age, where different realities are present, begins. When such transitions from one age to another are the subject of eschatological discussion, the phrase, "end of the world", is replaced by "end of the age", "end of an era", or "end of life as we know it". Much apocalyptic fiction does not deal with the "end of time" but rather with the end of a certain period of time, the end of life as it is now, and the beginning of a new period of time. It is usually a crisis that brings an end to current reality and ushers in a new way of living, thinking, or being. This crisis may take the form of the intervention of a deity in history, a war, a change in the environment, or the reaching of a new level of consciousness.

Most modern eschatology and apocalypticism, both religious and secular, involve the violent disruption or destruction of the world; whereas Christian and Jewish eschatologies view the end times as the consummation or perfection of God's creation of the world. For example, according to ancient Hebrew belief, life takes a linear (and not cyclical) path; the world began with God and is constantly headed toward God’s final goal for creation, which is the world to come.

Eschatologies vary as to their degree of optimism or pessimism about the future. In some eschatologies, conditions are better for some and worse for others, e.g. "heaven and hell".