This dissertation explores how some girls use humour in their everyday lives—from the jokes they share to the limits and taboos of humour they negotiate and the media content they discuss. Humour is examined as both a playful practice and a serious resource in shaping friendship, identity, and belonging. Drawing on 10 months long ethnographic fieldwork at a youth centre, focus group discussions in two high schools, and an extensive corpus of media material, including social media clips, the study highlights the multiple ways humour draws on constructions of identity, authenticity, and norms. The analysis builds on critical humour studies, combining discursive psychology and an analysis of young people’s humour practices in social interaction with Billig’s (2005) view of humour as ambivalent and multifaceted—meaning that humour can both challenge and reinforce power structures, unite and exclude, resist and discipline. The thesis demonstrates how young people navigate these tensions in everyday interactions. A central finding is that the girls’ humour practices are diverse and deeply ambivalent. There is no single agreement on what counts as funny or what should not be joked about. Instead, the boundaries of humour are continuously drawn, crossed, and renegotiated in conversation. Much of this humour revolves around taboo topics, where participants jointly test the limits of acceptability. Through this, humour becomes a space where identity categories—such as gender, ethnicity, and place—are performed and negotiated. The study shows how humor can transform identities often dismissed as humorless, for instance “women”, “feminists”, or “Muslims” into common reference points for shared laughter. The thesis further shows how humour plays a key role in how authenticity is negotiated in interaction. Rather than being fixed, authenticity is shown to be relational and context-dependent. This becomes visible, for example, in discussions about the “Orten” identity, where ethnicity, place, and loyalty intersect. The girls’ reflections reveal how authenticity is judged not only through language, but also through performance, consistency, and belonging. Friendship emerges as a key arena where humour plays a central role. Humour both strengthens solidarity and manages disagreements. Laughter, even when subtle, can signal alignment, resistance, or hesitation. By analysing these dynamics, the dissertation demonstrates how humour is central to the everyday work of maintaining and negotiating friendship. Overall, this dissertation contributes to critical youth studies by challenging simplified portrayals of young people as either subversive or conformist, and by positioning humour as a crucial lens for understanding how identity and belonging are negotiated in everyday life. It argues that young people’s humour deserves to be taken seriously in its own right, rather than as a projection of societal or researchers’ expectations. By focusing on girls’ humour practices and their conversations about humour, the study offers new insights into how humour mediates identity, authenticity, and belonging in contemporary youth culture.