Walter Lippmann was an influential journalist and political theorist of the twentieth century. A Preface to Morals, his most well-known and influential book, was first published in 1929.

In A Preface to Morals, Lippmann argues that in modern society traditional religious faith has lost its power to function as a source of moral authority. He asserts that ancient religious doctrine is no longer relevant to the conditions of modern life: governments have become increasingly democratized, populations have moved from rural to urban environments, and tradition in general is not suited to the dictates of modernity. Further, the democratic policy of the separation of church and state has created an atmosphere of religious tolerance, which suggests that religious faith is a matter of preference. In addition, the development of scientific method has created an atmosphere of doubt as to the claims made by religious doctrine.

Lippmann offers humanism as the philosophy best suited to replace the role of religion in modern life. He notes that the teachers of humanism are the wise men or sages, such as Aristotle, Buddha, Confucius, Plato, Socrates, and Spinoza, and that it is up to the individual to determine the value of their wisdom. He goes on to observe that one of the primary functions of religion is to teach the value of asceticism, or voluntary self-denial, as essential to human happiness. Lippmann describes an attitude of "disinterestedness" as essential to the development of a humanistic morality. Disinterestedness, for Lippmann, is an approach to reality that puts objective thought before personal desire. He claims that the role of the moralist in modern society is not, as in traditional religions, to chastise and punish but to teach others a humanistic morality that can fulfill the human needs traditionally filled by religion.

Lippmann's central themes in A Preface to Morals concern religion, modern society, moral authority, and humanism.