The potato, as the fourth most important world food crop, continues to stimulate research activity in commercial and academic sectors alike. Important objectives of this research are the factors regulating assimilate allocation to storage organs (sinksource relationships) and the mechanisms controlling assimilate conversions into storage products in the tubers. Of the tuber storage products, starch is of primary importance, accounting for up to 70% of tuber dry matter. It is the most important source of calories in the animal and human diet and provides a starter material for the preparation of more than 500 different commerical products. This chapter aims to update our understanding on tuber formation and on the most important metabolic processes occurring during tuber development. Particular emphasis has been given to the import and metabolism of sucrose, its conversion into starch and starch granule assembly. Substantial progress in these areas has been made in the past few years thanks to recombinant gene technology, and this will be reviewed here. For a more detailed description of the advances in potato transgenic biology, which is beyond the scope of this chapter, the readers are referred to other parts of this publication or to recent reviews (1,2).