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.

Mr. Wildenstein, who holds dual French and American citizenship, is enmeshed in at least a half-dozen lawsuits; some, provoked by the raid, are being brought by heirs who claim the artwork was stolen from their families.

Also seeking answers is the Académie des Beaux-Arts, a prestigious French cultural society that has filed a legal complaint seeking an inquiry about a missing painting; Mr. Wildenstein’s father, Daniel, and grandfather Georges were elected members.

Mr. Wildenstein has declined to speak publicly about the inquiry or the suits. His newly hired spokesman in Paris, Matthias Leridon, said by telephone on Friday that Mr. Wildenstein “will not answer by using the media.”