Teleological and deontological approaches to topics vary by their focus, with teleological approaches based on intended end effects and deontological approaches based on adherence to set rules. These terms are most often found together in the study of ethics. Teleological ethics are also often referred to as consequentialism.
Teleology extends beyond just ethics, and refers to any aspect of existence with a definite end, whether in human behavior or in nature. For instance, a teleological view of animals proposes that current animals are, in some sense, an intended end of evolution or creation. Deontology, on the other hand, is solely concerned with ethical questions.
Deontology, as a formal ethical model, is the older of the two, with the best-recorded example of antiquity being divine command theory. This theory states that an action is good or evil depending on whether it corresponds to rules set by a deity. The famous philosopher Kant, however, provided a different form of deontological ethics, whereby the morality of an action should be judged by whether the actor would desire that the morality justifying that action be universal.
Teleological ethics are much newer. One version, utilitarianism, was created by John Stuart Mill, and states that the most moral action promotes the greatest good for the greatest number of people. Conversely, actions that create a general net unhappiness are immoral.