This study claims that the most comprehensive understanding of Karl Rahner's religious inclusivism can be obtained through his approach to atheism as a theological and philosophical problem and through his views on the possibility of the salvation of atheists. Based on this claim, this study examines Rahner's discussion of atheism and the question of the possibility of the salvation of atheists from theological, existential, and epistemological aspects. First, it discusses Rahner's approach to atheism which he regards as a threat Christianity is faced by specifically in the modern era. Then, it analyses Rahner's concept of anonymous Christianity, namely his theory of salvation with a focus on the philosophical and anthropological concepts he uses in the construction of this theory. Finally, it examines Rahner's interpretation of atheism as one of the relationship forms between the human being and God and his application of his epistemological understanding in interpreting atheism.