Forward defense is not a new concept. It is rather traditional, coming from the Cold War and implying, originally, the nuclear posture and strategy. Following the issuance of the Madrid NATO Strategic Concept and Vilnius statement that not an inch of the Alliance’s territory will fall under the control of the opponents, a new approach to forward defense is needed to cope with the multiple shifts in the security environment: Russian war of aggression, the change of technological generation, dilemmas of resources and apabilities, limits and multiple challenges from the international environment with superposed simultaneous crises. The perspective of possible attacks on NATO territory – in the next 2-3-5-8 years – requires a review of the concept and, consequently, of the political decisions, strategic planning, enforcement of those decisions, and development of forces and capabilities on the ground. Combining nuclear flexible capabilities, a strategy of massive retaliation with conventional forces and deterrence by reinforcement, deterrence by denial, forward presence, rapid projection capabilities, resolution, effective decisionmaking, and forward posture, we could build a new, updated doctrine of forward defense. However, the debate has to consider what is theoretically developed, technically feasible, politically acceptable, financially sustainable, and strategically credible in the „new forward defense” for granting inviolability of allied territory. The basic limitation is to define and refine forward defense without a reconsideration beyond existing means.