Facebook CEO Mark Zuckerberg and his wife Priscilla Chan vowed today to “spend our lives doing our small part to help” solve the world’s problems — in part by giving 99% of their Facebook shares, now worth $45 billion, to worthy causes.

They made the announcement in an open letter to their new daughter, Maxima.

“As you begin the next generation of the Chan Zuckerberg family, we also begin the Chan Zuckerberg Initiative to join people across the world to advance human potential and promote equality for all children in the next generation,” they say. “Our initial areas of focus will be personalized learning, curing disease, connecting people and building strong communities.”

Although the effort is “a small contribution compared to all the resources and talents of those already working on these issues,” the new parents say they “want to do what we can, working alongside many others.”

Wall Street probably doesn’t have to worry that the stock gifts will depress Facebook’s share price. Zuckerberg won’t sell or give away more than $1 billion of stock each year over the next three years, the company notes in an SEC filing. He also “intends to retain his majority voting position in our stock for the foreseeable future” and will publicly disclose sales and gifts.

“I will continue to serve as Facebook’s CEO for many, many years to come,” Zuckerberg says in the open letter, “but these issues are too important to wait until you or we are older to begin this work. By starting at a young age, we hope to see compounding benefits throughout our lives.”

Zuckerberg owns about 4 million of Facebook’s Class A shares and 419 million Class B shares.

“We’ll share more details in the coming months once we settle into our new family rhythm and return from our maternity and paternity leaves,” the couple says in the open letter.

But the effort to promote human potential and equality will require “long-term investments over 25, 50 or even 100 years. The greatest challenges require very long time horizons and cannot be solved by short term thinking.”

Among other things, they hope to “engage directly with the people we serve,” build technology, “participate in policy and advocacy to shape debates,” back independent leaders, and “take risks today to learn lessons for tomorrow.”