Mitigation of greenhouse gases in the land sector is complex and has a unique set of challenges. The most significant challenges arise from the geographically diffuse nature of the emissions sources (compared to, for example, point-based energy sources of emissions), the vast array of potential management responses, the ongoing effects of past actions, the interaction of human and natural processes, and the strong influences of policy and markets. These factors result in a large number and diversity of actors involved, temporal variability in emissions sources and volumes, and higher uncertainty associated with the processes generating the emission reductions. Because of this, achieving large-scale mitigation in the land sector requires collective action involving multiple stakeholders undertaking different activities. This paper synthesizes several lessons learned in efforts to develop systems that integrate incentive mechanisms at multiple scales. It illustrates many lessons through examples and the appendix presents individual case studies from a variety of geographies, Acre (state in Brazil), Australia, Brazil (Amazon), the Democratic Republic of Congo (DRC), Guatemala, and Zambia. The hope is that the experiences of emerging 'nested' systems can provide inspiration to countries developing REDD systems, particularly those which seek to catalyze across a landscape local actions that contribute to national mitigation. The objective of this paper is to share a few lessons from nested systems. While there are many positive benefits to nesting, experience suggests that countries struggle with development of nested systems. Very few have been operationalized (with exception to a few developed countries, such as Australia and New Zealand), although several REDD nested systems are now emerging. Section two explores four high-level 'typologies' that countries may consider when developing a nested system. Section three summarizes three key technical challenges that countries face: alignment of measurement systems, reference levels, and double counting. Both sections illustrate options using real-world examples from countries pioneering nested approaches and explain why certain choices were made. The paper concludes with thoughts on overall lessons learned, recognizing that the journey is still young.