This article investigates the integration of smallholders into voluntary certification schemes, exemplified by smallholder certification under the Roundtable on Sustainable Palm Oil in Indonesia (RSPO). It identifies the main barriers to the adoption of standards by smallholders and the specific compliance challenge in the context of RSPO smallholder certification, thereby contributing to the growing literature on the effectiveness of voluntary sustainability standards. It discusses findings on smallholder certification, focusing on antecedent variables as potential adoption determinants at the level of smallholders, smallholder organization, and the institutional context. The empirical findings suggest that smallholders, and specifically independent smallholders, often lack both the information and the degree of organization that certification demands. The article also identifies the most important compliance challenges for independent smallholders in relation to land titles, seedlings, pesticide usage, fertilization, and documentation and outlines how smallholders can be supported so that they can be included in certification schemes.