Stock Exchange Electronic Trading Service

The automated trading system introduced in 1997 for the largest companies quoted on the main list of the London Stock Exchange. Trades through SETS match buyers and sellers automatically, cutting out the need for a market maker, theoretically meaning a narrower bid-offer spread. Smaller companies continue to use the SEAQ quote book system, with market makers quoting prices to brokers and trades being done on a semi-automatic rather than fully-automatic basis.