This document provides an overview of deontological ethics as a normative ethical theory. It discusses key concepts in deontological thinking such as duty, intention-based morality rather than consequence-based morality, and categorical imperatives. It examines Immanuel Kant's deontological theory in depth, including his notions of good will, duty, and the categorical imperative. It outlines strengths and criticisms of Kantian ethics. Finally, it briefly introduces the deontological theory of W.D. Ross and the concept of prima facie duties.