Northern Europe is not at peace. The battle is real and far more dangerous than the public has grasped. In this war, there are no frontlines. Attack vectors shift daily, probing weaknesses, exploiting vulnerabilities, and seizing opportunities. The weapon of choice is what we in the West call hybrid warfare, targeting our institutions, our infrastructure, our alliances, and our minds. Resilience is necessary, but not sufficient, to win this hybrid war. This book shows how countries on the northern flank are strengthening national capabilities and deepening cross-border cooperation to detect, disrupt, and respond to hybrid threats—offering a blueprint for hybrid deterrence.