On May 18, 2022, the Swedish and Finnish NATO ambassadors formally submitted their countries’ membership applications to the alliance. In doing so, they ended decades – in Sweden’s case, centuries – of military nonalignment and overlapping but varied security arrangements in the Nordics and Baltics. Sweden and Finland, whose bilateral defense cooperation has deepened substantially in recent years, will now contribute to NATO’s defense of the Arctic and the Baltic Sea region. In this anthology, launched in cooperation between Stockholm Free World Forum and Konrad Adenauer Stiftung, writers from Sweden, Finland, and beyond explore how Sweden and Finland will adapt to NATO and vice versa. The chapters deal with topics such as how Sweden and Finland will contribute to burden sharing and specialization within NATO, what lessons can be drawn from past enlargements, and how Sweden and Finland can help the alliance deal with hybrid threats.