In this paper we discuss global climate change mitigation that builds on existing unilateral actions to deliver ever deepening emission cuts over time. A wide array of unilateral environmental measures have been documented. We discuss the rationale for such measures and argue that unilateral initiatives have the potentialto generate positive spillover e¤ects both within and across countries. Using a simple dynamic model of learning, we show how global negotiations can accelerate convergence to a global low emissions regime by building on and strengthening the positive spillovers inherent in unilateral initiatives.