Sustainability scholars frequently advocate for stewardship as a strategy to foster sustainable development. Stewardship broadly refers to the wise and responsible use of nature, and is considered necessary to ensure the long-term wellbeing of humans and that of life in general. In the academic literature local resource users, like hunters, farmers or fishers, are widely acknowledged to act as stewards of the natural environments their livelihoods depend upon. Research shows that this group of people often are able to use natural resources in a sustainable manner, and that their knowledge of how to do so can improve natural resource management. However, research also emphasizes how different local resource users have different potential to steward natural environments. There is thus a need to better understand what stewardship among local resource users entails more concretely as well as when and how it fosters environmental sustainability. In this thesis, I study stewardship in the case of Swedish Baltic small-scale fisheries. I conceptualize stewardship as an interaction between fishers and the social-ecological context in which they are embedded. This conceptualization implies that stewardship does not exist or emerge from within fishers themselves, but is created, formed and realized through fishing practices. I further define and analyze stewardship using a framework composed of three dimensions: care, agency and knowledge. My findings are contained in four papers. Paper I presents a theoretical model of how local resource users respond to social and ecological change, and shows the model’s empirical relevance. Paper II gives an overview of the diversity and development within present-day Swedish Baltic small-scale fisheries. Paper III investigates the historical development of a Swedish fishery that targets the critically endangered European eel (Anguilla anguilla). Paper IV focuses on fishers’ knowledge and assesses how this knowledge can be applied in fisheries science and management. The papers collectively demonstrate the contextual nature of stewardship and showcase how stewardship varies over time as well as between fishers. The findings illustrate the ambiguous link between stewardship and environmental sustainability, they support the notion that fishers’ knowledge can improve fisheries management, while also suggesting that future research needs to pay more attention to how stewardship is empirically manifested. Overall, the thesis advances the understanding of stewardship by highlighting the social-ecological dynamics of local resource use.