Christel Boom (née Meerrettig, married name Christel Guillaume; 6 October 1927 – 20 March 2004) was an East German intelligence agent who worked for the Stasi to infiltrate the Social Democratic Party of Germany (SPD), the ruling party of West Germany from 1965 to 1983. Alongside her husband, Günter Guillaume, she helped to orchestrate the infiltration of the West German Chancellor Willy Brandt's government. The pair passed NATO and SPD information to the Stasi between 1969 and 1974. Their exposure as spies in 1974, dubbed the Guillaume affair, was part of a chain of events which led to Brandt's resignation as Chancellor the same year.
Along with her husband, Christel was arrested and imprisoned for seven years, before being released as part of prisoner exchange in 1981. On their return to East Germany, the pair returned to work for the Stasi, and were awarded the Order of Karl Marx. Christel divorced Guillaume shortly after, feeling betrayed that his confession had led to their imprisonment. She retired in western Berlin after German reunification, and died in 2004.