Like all animals, humans are programmed for survival. Fight or flight? Duck! Run for cover! Our reflex, when we register fear, is to protect ourselves. Architecture’s answer, “shelter,” is said to derive from sheltron, or “shield” + “troop”; phalanx. But what shields or defends can intimidate, exclude, and punish. Architecture is not just refuge, but target and weapon; buildings entrap, collapse, explode, segregate. This issue of Harvard Design Magazine explores how fear—of assault, of nature, of power, of the Other—shapes our physical world, and how the built environment provokes, prevents, or palliates fear. Today, we move about our cities and spaces warily, attuned to threats of violence, disease, economic crash. Sensations of dread, awe, vulnerability—both perceived and real—are mirrored and magnified by the people, objects, and media that surround us. In panic, we run toward and away from the structures and landscapes that figure in our fears; we succumb to lockdowns; we migrate, seeking safer worlds. All the while, we blind ourselves to the regimes of control enacted in the name of safety which ultimately encroach on our civil liberties. Our instinctive urge to hide under tables might save us when faced with a shooter, a bomb, or an earthquake, but more abstract threats ask our minds, not just our adrenaline, to intervene. Can we think our way out of fear? Design our way through dread? As the makers and inhabitants of this militarized “age of terror,” we reach for our “shields” automatically, often avoiding the deeper sources of fear. “Run for Cover!” suggests that maybe designers need to unlearn the shelter reflex. Fear can be a motivator for progress—not for walling in or walling out, but for imagining, configuring, and instrumentalizing spaces that foster coexistence, cooperation, and trust.