The thesis examines the atheistic development visible in the Swedish Human-Ethical Society’s (HEF) journal 1979 to 1999. It argues that HEF:s atheism from a diachronic perspective is best understood with the regards both to its religious criticisms, as well as to the specific outlook on life that the organisation developed over time as a secular alternative to religious belief-systems. The thesis further stresses the importance of comprehending atheism as a pluralistic system of thought that throughout history – as well as in present day – have taken a variety of different formations. Hence, atheism is not seen as possessing one single overall essence. The result of the study show that several developmental patterns can be made visible in HEF:s atheism throughout the period. The organisations religious criticism changed regarding its objects, contents and rhetoric. From initially having its focus directed towards Christianity (Swedish Christianity in particular), HEF later to a larger extent directed their critical gaze towards what they regarded as fundamentalist ideological values. Over time the organisation also started to highlight atheism in a, according to their phrasing, more “positive” light. With this, HEF:s human-ethical life stance was given a more instrumental role in the organisations message to the public. The thesis argues that this development should be understood as a successive shift in the basis for HEF:s atheism. On a general analytic level this process is characterized as a move from scientific atheism to humanist atheism.