The situation of overlapping offset crediting programmes has not been well addressed or widely discussed in academic or policy dialogues. The policy question is whether a single activity can earn offset credits from more than one offset programme. Further, how do we assess the additionality and baselines for proposed activities in a situation with overlapping offset crediting programmes? This article applies the definitions and framework regarding additionality and baselines from Parts 1 and 2 of this series to this issue of stacking. It presents specific options for how to apply the concept of additionality to activities that could potentially stack offset credits and outlines a practical way forward for policy makers.