Throughout most of the series, whenever Barney is asked what he did for a living by his friends (such as Marshall in Life Among the Gorillas and Lily in World's Greatest Couple), he dismissively answers "please". This maintains the mystery of Barney's job throughout the series. Many strange events occur, such as Marshall in The Goat finding a contract detailing the poisoning of the water supply in Lisbon, Portugal in Barney's office, and Barney in Last Cigarette Ever mentioning that the company might murder him one day because of how much he knows, or that he won't be fired but he may end up missing with teeth and fingertips removed in Mosbius Designs.
Barney's job is revealed in Unpause, where it is also revealed that he has been responding honestly; PLEASE is an acronym ("Provide Legal Exculpation And Sign Everything") and Barney's job is being a legal scapegoat for his company's corrupt activities. He is essentially the company's "fall guy", signing various documents and becoming responsible for any illegal activity. Barney is secretly working for the FBI as an informant, with the intention of defeating his boss, who stole his girlfriend, Shannon, many years ago.