Anyone who has ever had the good luck to work in old archives knows how surprising they can be. A thick and unappetizing file might, with patience, yield a wealth of interesting detail; a pile of yellowed papers can contain the solution to an old riddle.

Recently, an amateur archivist stumbled across the letters of Otto Frank, Anne Frank's father, in a collection of documents that had been gathering dust in the YIVO Institute for Jewish Research for 30 years — proving that there was still more to learn, even about the most famous of all Holocaust victims, even in the middle of New York City.

Incredible though it sounds, there could be many more such surprises to come — given that the largest, most definitive and so far most inaccessible of Holocaust archives has yet to be opened to scholars or anyone else.

Officially known as the International Tracing Service, this archive contains files on more than 17 million people who passed through the concentration camps and forced-labor camps of the Third Reich, including Dachau and Buchenwald, as well as the camps of displaced persons that sprang up across Europe after the war. In 1955, the Allied powers deposited these records in Bad Arolsen, Germany. Legally, they were held under the aegis of an 11-nation treaty. In practice, they were put under the day-to-day management of the International Committee of the Red Cross (ICRC).

And there they remained, almost entirely under lock and key. Outside scholars were not permitted inside the Bad Arolsen archive. Victims who requested documents were put on a waiting list decades long. For many years the archive's director — a Swiss employee of the ICRC whose motives remain mysterious — successfully blocked all international efforts to open the archive further. He was aided by the German and Italian governments, probably because they feared that the documents could lead to a new wave of compensation claims. He was also aided by the fact that it's hard to get an 11-nation commission to do much of anything at all, especially an 11-nation commission that meets only once a year.

Last summer things changed: The commission finally decided to alter the treaty and to make digital copies of the documents available to member countries. Under a certain amount of international pressure, the ICRC fired the weirdly secretive archive director. Under quite a lot of international pressure, the German government had a change of heart. Some of the digitization is already underway. And yet — although commission members are meeting in Holland this week, supposedly to make final arrangements, it's still far from clear that they will finish the process soon.

Sixty-two years after the end of the Second World War, how can this be? In whose interest can it possibly be to keep Holocaust archives closed? It's fair to say some of the problems are purely technical: Though the United States, Israel, Poland and Luxembourg have ratified the necessary treaty changes, France, for example, has trouble ratifying treaties in an election year.

Other concerns may be more substantive: Some suspect the Italians are stalling because they fear the records will reveal just how many Nazis escaped through Italy after the war. Still others — including possibly the Germans — simply don't, in the words of Arthur Berger of the U.S. Holocaust Memorial Museum, "understand the urgency" of the issue.

And "urgency" is the right word: Hundreds of thousands of people are still waiting to see documents, and more of them die every day. If discussions go the right way this week, digital copies of documents could be available for some of them to read, in their own countries, later this year. If not, they may never see them at all.

Unexpectedly, the urgency is now also political. We live in a world in which the president of Iran can attract a slew of prominent Holocaust deniers to a conference in Tehran — and in which some of those Holocaust deniers point to the continued closure of the Bad Arolsen archive as evidence that the Allies want to conceal the "truth" about the Holocaust from the world.

Though it is tempting, as I've written before, to treat the events of 62 years ago as well-known history, that would be a mistake.

In fact, it is precisely because so many of the protagonists are now dead, precisely because everyone assumes everything has already been written and precisely because the Holocaust has become so thoroughly institutionalized that this archive must be opened. The European nations meeting this week must open the archive to ensure that a new generation, and all future generations, are able to rediscover the facts for themselves.

Anne Applebaum is a columnist for the Washington Post.