That's a very good question and one that successive generations of critics have been asking themselves. To date, Agatha Christie's The Mousetrap has been running continuously in London's theater district, the West End, since 1952. Indeed, it is officially the world's longest-running play, enjoyed by successive generations of theater-goers. And there are no signs that the popularity of this theatrical warhorse is in any way flagging.

So why is The Mousetrap so popular? One factor is the abiding popularity of its playwright, Agatha Christie. Christie's detective stories are as popular today as they always were, garnering millions of loyal fans who delight in their famous twists and turns. The Mousetrap itself has a famous twist ending—which I won't reveal here—and it has become something of a tradition for audience members to see if they can work out the ending before the final scene.

There's also a touristic element to the play's enduring success. Many visitors to London regard a trip to St. Martin's Theatre to see The Mousetrap as another item in their lengthy itineraries, along with visiting Madame Tussaud's or watching the Changing of the Guard at Buckingham Palace.

There are all kinds of reasons why The Mousetrap remains so popular. The simplest one of all is that it's a very well-made play, with lots of interesting characters—all of them with dark secrets—surprises, and plenty of Christie's trademark black humor.