Glycosylated natural products have served as reliable platforms for the development of many existing front-line drugs. In an effort to explore the contribution of the sugar constituents of these compounds, research groups have focused upon the development of chemical and enzymatic tools to diversify natural product glycosylation. Among the complementary routes available, in vivo pathway engineering, also referred to as 'combinatorial biosynthesis', is an emerging method that relies upon the co-expression of sugar biosynthetic gene cassettes and glycosyltransferases in a host organism to generate novel glycosylated natural products. An overview of recent progress in combinatorial biosynthesis is highlighted in this review, emphasizing the elucidation of nucleotide-sugar biosynthetic pathways and recent developments on glycosyltransferases.