This chapter examines the key ideas and concepts of ‘classical’ anarchist thinkers. Among the ideas associated with anarchism are: a belief in the potential of human nature, and a corresponding critique of arbitrary authority; a refusal of state authority; a rejection of the institution of private property; militant atheism; and an emphasis on the importance of revolutionary politics. The chapter first considers how anarchist views on human nature, the state, political action, private property, and religion vary, and where possible, what unites them. It then discusses recent critical responses to anarchism, particularly ‘post-anarchism’, and specific historical examples of anarchism. It also analyses the extent to which anarchism can be regarded as a cohesive political ideology.