Stephen Craig West FRS (born 11 April 1952) is a British biochemist and molecular biologist specialising in research on DNA recombination and repair.

He received the 2022 Royal Medal for 'discovering and determining the functions of key enzymes that are essential for DNA recombination, repair and the maintenance of genomes'.

After finishing his PhD, which he completed within three years, he moved to the United States to join the group led by Paul Howard-Flanders, one of the early pioneers in the field of DNA repair.

In the Howard-Flanders group at Yale University, West purified and characterised RecA protein, and in doing so discovered many key aspects relating to the way that cells mediate DNA-DNA interactions and strand exchange.

After moving to the UK in 1985, West continued his work in bacterial systems, and set about trying to identify cellular proteins capable of resolving recombination intermediates.

His laboratory discovered that the Holliday junction resolvase activities of MUS81 and GEN1 are regulated so that they act late in the cell cycle to ensure chromosome segregation.

His laboratory also discovered that Aprataxin, which is defective in a progressive neurological disorder known as Oculomotor apraxia, is a 5'-deadenylase that removes AMP from 5'-termini following abortive DNA ligation.

Recently his laboratory described the high resolution structure of the RAD51B-RAD51C-RAD51D-XRCC2 (BCDX2) complex using cryo-electron microscopy, and defined its function in DNA repair and tumour avoidance.

As it is clear that DNA repair plays a critical role in the maintenance of genome stability and cancer avoidance, West’s work is significant in terms of understanding the molecular basis of human disease.