"Le Deuxième Sexe," written by Simone de Beauvoir and published in 1949, is a foundational text in feminist philosophy. The book explores the construction of women's identity and the societal roles imposed on them, arguing that women have historically been defined as the "Other" in relation to men. De Beauvoir examines various aspects of women's lives, including biology, history, and culture, to illustrate how these factors contribute to their oppression. The work emphasizes the importance of women's liberation and the need for equality, making it a significant influence on feminist movements and gender studies.