Marcel Bloodthaer's sister's dress

The Museum of Modern Art is on a mission to become a leader in American and European Conceptual art from the 1960s and ’70s. This week it announced the acquisition of two important collections. One is from Seth Siegelaub, a publisher and dealer in Amsterdam who was an early supporter of artists like Vito Acconci, Robert Barry, Douglas Huebler, On Kawara, Joseph Kosuth, Robert Smithson and Lawrence Weiner. The collection includes examples of each.

The Modern also received 223 works created between 1966 and 1978 from the Brussels collectors Herman and Nicole Daled-Verstraeten. The collection, in a variety of mediums, includes 62 works by Marcel Broodthaers and prime work by artists like Dan Graham, James Lee Byars and Daniel Buren.

“You can’t find historical examples like this on the market,” said Christophe Cherix, chief curator of prints and illustrated books at MoMA. Mr. Cherix knew the Daleds had a collection, but it wasn’t until it went on view at the Haus der Kunst in Munich last summer that he realized its extent and importance. “It was a revelation,” Mr. Cherix said. “It fit like a glove with our collection. Almost nothing was redundant.”

The Daled collection is part gift, part purchase. Among the pieces that Mr. Daled has given MoMA is “Maria’s Dress,” a 1966 work by Broodthaers in which he borrowed his sister-in-law’s dress and hung it with a paper bag covered with eggshells. “When Mr. Daled saw it in a small gallery in Brussels right after it was made, he immediately bought it,” Mr. Cherix said. “The funny thing was, Broodthaers never expected it would sell, and as a result his sister-in-law never got her dress back.”