SAN FRANCISCO — Mark Zuckerberg, Facebook’s chief executive, and his wife, Dr. Priscilla Chan, last year said they would give 99 percent of their Facebook shares to charitable causes. Now they are putting a large chunk of that money to work.

The Chan Zuckerberg Initiative, the limited liability company into which Mr. Zuckerberg and Dr. Chan put their Facebook shares, on Wednesday said it would invest at least $3 billion over the next decade toward preventing, curing or managing all diseases by the end of the century.

While the Chan Zuckerberg Initiative has already made investments in charter schools and education start-ups, the money toward curing diseases represents the group’s first major initiative in science. The announcement was also a coming out of sorts for Dr. Chan, who has a big interest in health and was trained in pediatrics.

In a speech to introduce the health initiative at an event in San Francisco on Wednesday, Dr. Chan said the work to cure disease was in keeping with her organization’s mission to advance human potential and promote equality. She gave an emotional preamble, describing how a high-quality education helped her succeed as the daughter of Chinese and Vietnamese immigrants.