This figure shows a timeline of the development of cephalosporin generations. It begins on the left in 1960 with the semi-synthesis of 7-ACA and continues showing the introduction date and structure of each successive generation of cephalosporins and ending with the development of 5th generation cephalosporins in 2013. New structures added to each generation are shown in blue. Above the structures is a blue arrow running from left to right labelled human chemical evolution. On the left of this arrow is Gram-positive activity and on the right is broad-spectrum activity to illustrate how subsequent generations of cephalosporins have changed their activity.