Interceptions are predominantly made by the secondary or the linebackers, who are usually closest to the quarterback's intended targets: the wide receivers and tight ends. Less frequently, a defensive lineman may get an interception from a tipped ball, a near sack, a shovel pass, or a screen pass. As soon as a pass is intercepted, everyone on the defense immediately become blockers, helping the person with the interception get as much yardage as possible and maybe a touchdown, while everyone on the offense becomes the defense, and may attempt to tackle the ball-carrier.
An interception is commonly referred to as a "pick" by football commentators. An interception returned for a touchdown is commonly referred to as a "pick-six", and can quickly change momentum in a game. The term "oskie" historically has also been used to describe an interception. According to www.oskie.com, General Robert Neyland, head coach of the University of Tennessee Volunteers for three stints (1926-1934, 1936-1940, 1946-1952), made it one of his Seven Maxims of Football: "Ball, oskie, cover, block, cut and slice, pursue and gang tackle...for this is the winning edge."
Here is a link that tracks current and historic Interception leaders for American/NFL football:
Paul Krause holds the record for most career interceptions, and is tied for third place for most interceptions by an NFL rookie in his first season, with 12. He played his first three years in the NFL from 1964 to 1967 with the Washington Redskins but was quickly traded to the Minnesota Vikings, where he spent most of his career. Krause played until 1979 and appeared in four Super Bowls with the Vikings (though he never won), and was inducted into the Pro Football Hall of Fame in 1998.
Ty Law has 50 interceptions and remains active in the NFL. Champ Bailey, who played for the Washington Redskins and currently plays for the Denver Broncos, had 10 interceptions in 2006 and has a career total of 43. Safety Darren Sharper, most notable for playing 8 seasons with the Green Bay Packers, has a career total of 51 interceptions. Strong Safety Sammy Knight has 42 interceptions in his career. (as of week 14 of the 2007 season)
James Johnson was named the Outstanding Player of the 95th Canadian Football League Grey Cup on Nov. 25, 2007 after intercepting a record three passes, including one for a 30-yard touchdown. His defensive efforts helped lead the Saskatchewan Roughriders to a 23-19 victory over their CFL Prairie rival Winnipeg Blue Bombers. In fact, it was the first time since 1994 that a defensive player was awarded the Grey Cup's top individual title. For Johnson, the $10,000 cash prize is quite a windfall for someone who used to work "12 hours a day, every day at an oil refinery in Los Angeles. His most notable interception of the game was when he intercepted Ryan Dinwiddie's final pass and secured Saskatchewan's victory.
Ed Reed of the Baltimore Ravens holds the record for the longest interception return, 106 yards against the Cleveland Browns on November 7th 2004. He also holds the record for most interception return yards in a single season, 358.
Brett Favre holds the record for most career interceptions thrown: 292. Favre's first pass in an NFL regular season game resulted in an interception returned for a touchdown. Favre's last pass as a Green Bay Packer was an INT as well thrown to Corey Webster of the New York Giants in the 2008 NFC championship game to lose the game.