St Martin-in-the-Fields is an English Anglican church at the north-east corner of Trafalgar Square in the City of Westminster, London. It is dedicated to Saint Martin of Tours. There has been a church on the site since at least the medieval period. It was at that time located in the farmlands and fields beyond the London wall, when it was awarded to Westminster Abbey for oversight.
It became a principal parish church west of the old City in the early modern period as Westminster's population grew. When its old structure was found to be near failure, the present building was constructed in an influential neoclassical design by James Gibbs in 1722–1726. The church is one of the visual anchors adding to the open-urban space around Trafalgar Square.