After 23 Years, 'Simpsons' Hits 500th Episode

The TV show The Simpsons is airing its 500th episode on Sunday. In its run, the show has aired more than 170 prime-time hours and had 23 seasons with hundreds of guest stars. Melissa Block and Robert Siegel offer a look back on the long-running animated series with insight from a few of the people who know it best: the writers.