This chapter presents an overview of Martin Luther’s doctrine on professional activities developed in On the Freedom of a Christian, To the Christian Nobility of the German Nation, and some Postils. This doctrine will eventually be collected in the Augustan Confession, stating the obligation to attend diligently to one’s own Beruf (calling) and paving the way for a general principle of professional ethics. In analysing the author’s elaboration on calling, his insistence on the subjective intention of the performer is highlighted. Luther does not make any objective connection between social-economic status, moral quality, and professional competence. However, his elaboration is key to shedding light on professional activity being viewed, and lived, as the main vector of self-realization.