"Follow the money" is a catchphrase popularized by the 1976 drama-documentary motion picture All The President's Men, which suggests a money trail or corruption scheme within high (often political) office.
For the film, screenwriter William Goldman attributed the phrase to Deep Throat, the informant who took part in revealing the Watergate scandal. However, the phrase is mentioned neither in the non-fiction book that preceded the film, nor in any documentation of the scandal. The book does contain the phrase "The key was the secret campaign cash, and it should all be traced," which Woodward says to Senator Sam Ervin. This may have been condensed to the phrase "follow the money" in the screenwriting process.
The phrase Follow the money was mentioned by Henry E. Peterson at the 1974 Senate Judiciary Committee hearings as Earl J. Silbert was nominated to U.S. Attorney. A 1975 book by Clive Borrell and Brian Cashinella, Crime in Britain Today, also uses the phrase.
In the 2002 episode "Game Day" (number 9 of the first season) of The Wire, Detective Lester Freamon uses the phrase when investigating the dealings of a Baltimore criminal gang to explain the political difficulty of investigating organized crime, saying "You follow drugs, you get drug addicts and drug dealers. But you start to follow the money, and you don't know where the fuck it's gonna take you".