This paper surveys forest carbon standards for their insight to relevant results-based payments for REDD+. The aim is to assess how different results-based initiatives deal with common Reference Level (RL) design problems in order to inform REDD+ negotiations and policymakers. RLs set a performance benchmark for mitigation activities by providing a reference point, or baseline, to which current and actual efforts can be compared throughout a pre-determined timeframe. The report is intended to serve as an overview of options for constructing RLs and enhance understanding of how their different forms and function will impact the overall design of REDD+ mechanisms. It concludes that although RLs in all the existing standards and initiatives share a core foundation (the idea of a performance benchmark or reference point for measuring results of mitigation efforts), they often have different nuances and functions depending on the context in which they apply and the purpose they serve.