Led Zeppelin weren't sure they'd ever return to the road after their disastrous 1977 North American tour. Jimmy Page's heroin addiction was taking a severe toll on the guitarist, and 70 fans were arrested in Cincinnati when they tried to rush the gates of the Riverfront Coliseum without tickets. (Two years later, 11 Who fans died in a pre-concert stampede at the same venue.) A bigger riot broke out in Tampa, Florida when a thunderstorm ended the concert prematurely. On top of all that, a vicious brawl broke out backstage at an Oakland show between Bill Graham's staff and Led Zeppelin's management. It resulted in hospitalizations, arrests and a huge lawsuit.
But all of that paled in comparison to what happened a couple of days after the Oakland fiasco: Robert Plant learned that his five-year old son Karac died of a stomach virus. The rest of the tour was immediately called off, and nobody knew what the future held for Led Zeppelin.
The band reconvened a year and a half later later to begin work on In Through the Out Door, but Plant had zero interest in another tour. Zeppelin hadn't played in England since 1975, creating a massive build-up of interest. After much internal debate, the group agreed to best way to handle the situation was to book two enormous outdoor concerts in Knebworth, England in August of 1979.
Opening acts for the shows included Todd Rundgren and Utopia, Southside Johnny and the Asbury Jukes, the Marshall Tucker Band and the New Barbarians featuring Keith Richards, Ron Wood and Ian McLagan. Led Zeppelin were a little rusty and clearly nervous, but few fans cared – they were overjoyed to finally see the band back in action. Here's a video of "Over the Hills and Far Away" from the first Knebworth show on August 4th, 1979.
Led Zeppelin toured mainland Europe in the summer of 1980. An American tour was booked for later that year, but it was canceled when drummer John Bonham died. They wouldn't play England again until their reunion show at London's 02 Arena in 2007. At this point, it seems quite likely they will never play again.