This primer is designed to provide you with a solid understanding of what Payments for Ecosystem Service (PES) are and how PES deals work. It is intended for an audience interested in exploring the potential of PES either as prospective PES sellers themselves or as staff of organizations that work directly with communities or landowners who may be interested in PES. The primer should be read before you set out to design a PES deal, as it provides guidance on conditions under which PES is most relevant and likely to succeed. It should also be read sequentially, as concepts defined in the early pages are built upon later.