In 2025, Finland, Poland, and the Baltic states announced their withdrawal from the Ottawa Treaty and the reintroduction of the anti-personnel mine (APM) into their defences. Bordering Russia, the countries justified the decision by citing the deterioration in the security situation. Using Finland as a case study, this report examines more closely the factors that enabled the ban on APM in the past and prompted its reintroduction in 2025. The identified factors include political shifts in Finland and internationally, notably in the United States; Finland's domestic demographic and economic conditions; and, most importantly, changing assessments of Russia's strategy and tactics in light of lessons from the war in Ukraine. In addition, the report explores and lays out the implications of reintroducing APM for collective defence within NATO. Ensuring interoperability will pose a particular challenge for cooperation between Finland and Sweden, given the two countries' extensive defence ties and the strict Swedish interpretation of the Ottawa Treaty. The allies will therefore need to find ways to balance operational needs with their obligations under international law. Finally, the report reflects upon a potential shift in the mode of security policymaking in Finland and upon APM use based on lessons from Ukraine.