PARIS — On a mild day in January, French police investigators poured into the regal Right Bank building of an art research center called the Wildenstein Institute and began sifting through a substantial trove of artworks there.

It was the third police raid on the institute, and at the end of it the investigators carried away armloads of art, including Degas drawings, a bronze sculpture by Rembrandt Bugatti and an Impressionist painting of a Normandy cottage by Berthe Morisot. All had been reported missing or stolen, some by Jewish families whose property was looted by the Nazis, and others by heirs who said their treasures had vanished during the settlement of their family estates.

The seizure of about 30 works has put an uncomfortable focus on the Wildenstein family, a discreet dynasty of French Jewish art dealers stretching back five generations whose name has long been one of the most prestigious in the international art world.

At the center of the current wave of troubles is Guy Wildenstein, 65, the president of Wildenstein & Company, an operation with spaces in New York, Tokyo and Paris. The family has faced controversies in the past, and lawsuits too, but never of the number or magnitude of those on the docket now. Mr. Wildenstein was summoned to Paris from New York to face questioning this week by French antifraud investigators who discovered the artworks while investigating money-laundering and tax evasion alleged in a criminal lawsuit against him.