This series of monographs intends to draw attention to a number of species which have been neglected in a varying degree by researchers or have been underutilized economically. It is hoped that the information compiled will contribute to: (1) identifying constraints in and possible solutions to the use of the crops, (2) identifying possible untapped genetic diversity for breeding and crop improvement programmes and (3) detecting existing gaps in available conservation and use approaches. Mashua (Tropaeolum tuberosum R. & P.), along with several potato species (Solanum spp.), ulluco (Ullucus tuberosus Caldas) and oca (Oxalis tuberosa Molina), pertains to the group of edible tuber crops indigenous to the cool-temperate Andes. Mashua is economically much less important than the other Andean tuber crops, but, as this monograph is intended to show, the crop's potential has been largely overlooked and opportunities for wider use within its native range and beyond have remained unexplored (Fano and Benavides 1992; Hermann and Heller 1997). Mashua contributes to tuber diversity, resulting in greater production stability in the heterogeneous Andean environments.