Lysine is an essential amino acid for mammals but its concentration in cereals, one of our main food sources, is low. Research over the past 40 years has unraveled many biochemical and molecular details of the aspartic acid pathway, which is the main route of lysine biosynthesis in plants. However, genetic manipulation of this pathway has not been successful at producing high-lysine seeds. This is because lysine, instead of being accumulated, is degraded via the saccharopine pathway. Recent work has increased our knowledge of this pathway, including both the enzymes involved and their regulation.