Given its vast land resources and favorable water supply, the Democratic Republic of Congo's (DRC) natural agricultural potential is immense. However, the economic potential of the sector is handicapped by one of the most dilapidated transport systems in the developing world (World Bank, 2006). Road investments are therefore a high priority in the government's investment plans, and those of its major donors. Whilst these are encouraging signs, very little is known about how the existing road network constrains agricultural and rural development, and how these new road investments would address these constraints. To inform this issue the present paper primarily employs GIS-based data to assess the impact of market access on agricultural and rural development (ARD). Compared to existing work, however, the paper makes a number of innovations to improve and extend the generic techniques used to estimate the importance of market access for ARD. First, the DRC road network data is augmented with survey-based data from Minten and Kyle (1999) on agricultural transport times to calculate improved “market access” measures for the DRC. Second, we follow Dorosh et al (2009) in estimating the long run relationship between market access and agricultural production, although we also investigate the relationship with household wealth. Finally, we run simulations of how proposed infrastructure investments would affect market access, and how market access would in turn affect agricultural production and household wealth.