The Coulomb barrier occurs at the quantum interface between the strong and the electromagnetic fundamental forces. Within the barrier, the intense attraction of the strong force confines nucleons and quarks within the atomic nucleus. Beyond the barrier, the electromagnetic force predominates owing to the net positive charge of the nucleus and its tendency to repel other nuclei. Overcoming the Coulomb barrier is the central goal of nuclear fusion, and an effective model of the barrier can only accelerate the achievement of this potential source of clean and abundant energy.