For many years, the issue of the legal form of the new climate agreement has hovered over the international negotiations. Countries have insisted on first discussing substance. Indeed, it is here that the main divergences remain. However, one year out from the Paris climate conference, it is time to open the discussion on the legal form of the final agreement. The issue of legal form is often reduced to the negotiation of a ‘binding’ or ‘non-binding’ agreement. The bindingness of an international environmental agreement however depends on multiple parameters. We propose four parameters to be considered: the form of the core agreement; the ‘anchoring’ of commitments; mechanisms for transparency, accountability and facilitation; and mechanisms for compliance. Parties should assess pros and cons of these options, and the agreement should be optimised across all four, combining flexibility and credibility.