This thesis examines the index effect in the Nordic markets, a phenomenon where stocks added (removed) to an index tend to experience positive (negative) abnormal returns. The study follows an event study methodology, and the results show that Nordic stocks exhibit only a temporary index effect in abnormal returns before the announcement date and during the effective date, with no significant permanent impact on price and volatility. The Price Pressure Hypothesis supports the findings and some evidence that speculation is driving the abnormal returns before the announcement date is provided. These findings imply that the index effect in Nordic markets exists but is rather short-lived and largely driven by temporary demand-supply imbalances. This contributes to the understanding of market efficiency in smaller markets and highlights a potential price anomaly that investors can exploit.