Every year, the Editorial Committee of each Annual Reviews series asks an internationally distinguished researcher to prepare a prefatory article for the volume being planned. It was an easy choice for us to seek a contribution from John B. Fenn (b. 1917), who since 1994 has been a professor of analytical chemistry at Virginia Commonwealth University in Richmond, Virginia. Few people have achieved the originality and the impact that John Fenn has shown in his development of new instruments for chemical analysis. Anyone using supersonic jet expansions or electrospray ionization owes a huge debt to this special individual, who was awarded the Nobel Prize in Chemistry in 2002. A full account of the development of electrospray ionization may be found in Fenn's 2002 article in the Journal of Biomolecular Technique.
