Deontological ethics or deontology (from Greek δέον, deon, "obligation, duty"; and -λογία, -logia) is an approach to ethics that judges the morality of an action based on the action's adherence to a rule or rules. Deontologists look at rules and duties.

It is sometimes described as "duty" or "obligation" or "rule" - based ethics, because rules "bind you to your duty" The term "deontological" was first used in this way in 1930, in C. D. Broad's book, Five Types of Ethical Theory..

Deontological ethics is commonly contrasted with consequentialist or teleological ethical theories, according to which the rightness of an action is determined by its consequences. However, there is a difference between deontological ethics and moral absolutism. Deontologists who are also moral absolutists believe that some actions are wrong no matter what consequences follow from them. Immanuel Kant, for example, argued that the only absolutely good thing is a good will, and so the single determining factor of whether an action is morally right is the will, or motive of the person doing it. If they are acting on a bad maxim, e.g. "I will lie", then their action is wrong, even if some good consequences come of it. Non-absolutist deontologists, such as W. D. Ross, hold that the consequences of an action such as lying may sometimes make lying the right thing to do. Kant's and Ross's theories are discussed in more detail below. Jonathan Baron and Mark Spranca use the term Protected Values when referring to values governed by deontological rules.