London Tube strike: How Londoners faced the disruption
All London Underground lines were suspended after thousands of workers went on strike.
About 10,000 workers from the Rail, Maritime and Transport (RMT) union walked out in a dispute over job losses and pensions.
Last-ditch talks to avert the strikes broke up after only 20 minutes.
Transport for London's (TfL) chief operating officer, Andy Lord, said: "I apologise to customers for this and understand they will be frustrated by this strike action, but urge them not to take it out on those who are trying to help.
"We haven't proposed any changes to pensions or terms and conditions, and nobody has or will lose their jobs because of the proposals we have set out, so this action is completely unnecessary."
The RMT union has declared a second 24-hour strike will take place on Thursday, unless a deal can be reached.