This dissertation is the first historical work attempting to investigate queerness in interwar Poland in a comprehensive, contextualized manner. In doing so, it does not seek to answer Miłosz’s rhetorical question. Instead, it asks how the place and epoch in which the writer lived led him to conceptualize human sexuality in such a fluid way, interpreting literary circles of interwar Warsaw as “gay.” At its most basic level, this dissertation investigates the lives of queer individuals from various classes, social backgrounds, and settings across interwar Poland. Among them are a homosexual male couple from a borderland town, a queer soldier in the Polish army who was a hero of the Polish-Soviet War, a Greek-Catholic girl who fell in love with a Catholic nun, and crossdressing sex workers in the streets of Warsaw. The narrative of the dissertation places these queer microhistories within the broader political and social contexts of the time, illustrating how non-heteronormative sexualities became an increasingly visible topic in the nation’s life, transitioning from medical discourses to political, ideologically charged debates. While the queerness of prominent intellectuals in interwar Poland has been noted before, this dissertation discusses the social context of their sexual dissent. It also views these individuals, though loosely connected, as one of the many queer (or queerly-tinted) social networks of the time, focusing on the group’s class, gender, and politics. In addition to presenting queer life in interwar Poland, the dissertation attends to topics such as the emergence of the term “homosexuality” in the Polish language, the decriminalization of homosexual acts in 1932, and the escalating homophobia in public discourse during the late 1930s. Another focus of this dissertation centers on the issues of homosexual and queer subjectivities and communities. The work balances between microhistories and sources that illuminate the self-identifications of queer individuals and their perceptions of (homo)sexuality, and the formation of social networks based on shared sexual inclinations within which some queer individuals lived in interwar Poland. Lastly, addressing the dimension that inspired the title of this dissertation, it argues that nationalism is vital for comprehending queerness, queer subjectivities, and queer communities in interwar Europe during this period. Nationalist ideologies not only influenced and regulated the lives of individuals and groups, but they also made them think of themselves as homo- or heterosexual by defining social reality in terms of clear-cut, essentializing categories. In other words, the relationship between nationality and sexual identities is not only one of bidirectional influence but also of parallelism, similarity, and mutual constitution. “Sex in the Times of Nationalism” paints a complex, multilayered portrayal of queerness in interwar Poland, where the specter of the nation looms large, influencing the lives of individuals and entire communities, transforming their sexual and romantic opportunities and experiences. It suggests that 20th-century sexuality would be unrecognizable to us if not for interwar nationalism.