Leguminous cover crops can be used in the humid tropics to increase the production of subsequent food crops, through effects on nitrogen availability in the soil, suppression of weeds and/or changes in soil physical conditions. Nodulation, total root and shoot mass and depth of root development are important characteristics of cover crops. Root development of several cover crops is described here for two sites with acid soils, in S.E. Nigeria and S. Sumatera, Indonesia. Short-lived annual species have a higher shoot: root ratio than perennial species. Mucuna pruriens utilis had the most shallow root system, but good nudulation and, through its fast growth, it was best insuppressing weeds (in a 4-month period). Mucuna and Crotalaria juncea gave the best effect on a subsequent maize crop in an experiment on a dark grey alluvial soil in Malang, E. Java, Indonesia. Apart from being a source of N, the cover crops also had a positive effect on subsequent maize growth by increasing water storage in the soil and by improving root development of maize.