Andreas-Salomé wrote widely in philosophy, literary criticism fiction, and psychoanalysis. She was active and influential in intellectual circles at the turn of the century. In particular, her thought contributed to the ideas of Friedrich Nietzsche, Paul Rée, Rainer Maria Rilke and Sigmund Freud, all of whom she knew well.

Andreas-Salomé’s important study of the stages of Nietzsche’s thought, Friedrich Nietzsche in seinen Werken (1894), has the central thesis that his outer, intellectual life is an expression of his inner, psychological life. In her critique of his philosophical ideas, she argued that the Übermensch is both unattainable and destructive. Despite her critical remarks, she embraced much of his anti-foundationalist thought, including the rejection of universal moral truth.

Andreas-Salomé’s psychoanalytic writings bring together her early interest in religion and her later ideas on love, sexuality and femininity. In her theory of narcissism, love and sex are a reunion of the self with its lost half. Love is directed back at ourselves because the lost self is actually an ideal image created from ourselves. But the union of the self and the ideal image also represents a union of the individual self with Spinozan Nature (or God). With Nietzsche, she believed that God is dead, but she added that he has an afterlife in the exalted human feelings that endure after the ideal (God) created by humans is replaced. These life-enhancing feelings are characteristic of narcissistic love which constitutes, especially for women, a progressive expansion of the self.