This thesis investigates the impact of the resource rent tax announcement and its implementation in Norway. The dataset consists of daily returns for eight salmon farming companies. Half of these companies are affected by the tax, while the other half are not affected. Our sample period ranges from August 2, 2022, to February 1, 2023, which covers the announcement and implementation day. By applying a difference-in-differences approach, we measure the causal effect that the resource rent tax had on the returns of the affected companies (companies that operate in Norway), relative to the non-affected companies (those that operate outside of Norway). Our findings reveal a statistically significant, large negative return in the affected companies on the announcement day. Return on implementation day was close to zero. This result is consistent with efficient markets, where only new information should move stock prices
