This study develops criteria for classifying the actor groups shaping frontier development along the Transamazon Highway colonization project in the Brazilian Amazon, as a basis to improve understanding of their specific contributions to environmental degradation and socio-economic development. Based on an analysis of responses to questionnaires by 93 colonists representing different migration trajectories, production systems, socio-economic strategies and deforestation patterns, actor groups could be statistically classified according to their type of production and level of capitalization. A property size threshold discriminating small and largeholders in the study area is presented and compared with previous attempts to establish such a threshold. Largeholders practicing large-scale cattle ranching and smallholders practicing diversified family agriculture were found to be the two predominant colonist types. Smallholder farming practices were found to be more appropriate to the local environmental conditions than those implemented by cattle ranchers.