During the last three years the generation of stably transformed cassava plants having value-added traits has become a reality. Currently, two Agrobacterium -mediated transformation systems are routinely used to engineer cassava. These systems use either somatic embryos or friable embryogenic calli. This paper presents detailed protocols for the transformation of cassava using primary somatic embryos. The effects of explant types, tissue culture conditions, and bacterial and plasmid related factors on transformation efficiency are discussed.