Jeff Bezos is one of few US top billionaires who hasn't signed the Giving Pledge. Here's how much the Amazon CEO has given to charity

The $15 million donation went toward creating a center studying neurological disorders at Princeton's Neuroscience Institute. The Bezos Center for Neural Circuit Dynamics opened in late 2013 on Princeton's campus in New Jersey.

Bezos and his ex-wife, MacKenzie, are both graduates of Princeton University — Jeff Bezos studied electrical engineering and computer science, while MacKenzie Bezos majored in english.

Bezos and his wife at the time, MacKenzie, donated $2.5 million to a group called Washington United for Marriage. The group was raising funds at the time for a campaign for Referendum 74, a state referendum that would legalize same-sex marriage in Washington if approved.

The donation from the Jeff and MacKenzie Bezos reportedly doubled the organization's campaign fundraising. The referendum appeared on the ballot in November 2012 and was approved.

Bezos pledged a half million dollars to Worldreader, a nonprofit that supplies children in underdeveloped countries with access to digital books and e-readers. Bezos' donation went toward boosting the organization's programs in African countries, including Kenya, Ghana, Uganda, and Rwanda.

Bezos pledged to match up to $1 million in donations given to Mary Place during Seattle's annual GiveBIG day of philanthropy in 2016. Mary's Place, a nonprofit providing housing to Seattle's homeless, exceeded its $1 million goal that year, bringing the organization's fundraising total to more than $2 million.

Although this is the only donation Mary's Place has received from Bezos personally, Amazon has turned part of its office space in Seattle into a homeless shelter (pictured above).

The $1 million gift was the largest personal contribution ever to the nonprofit, which advocates and provides resources for journalists and the First Amendment rights. RCFP's executive director called the donation "an institution-changing gift" for the nonprofit.

Jeff Bezos owns the Washington Post, a historic newspaper he bought for $250 million in August 2013.

Bezos donated enough to fund the college education of 1,000 Dreamers, immigrants who were brought to the US as children. The $33 million donation came during a time when President Trump attempted to end the Deferred Action for Childhood Arrivals program — known as DACA — under which these children were protected from deportation and allowed to work legally in the US.

Bezos said the donation was a nod to his father, Miguel Bezos (pictured above), who fled to the US from Cuba when he was 15. He later went on to attend college and work as an engineer at Exxon.

Bezos' first major political donation was a $10 million donation to With Honor, a bipartisan PAC that backs military veterans running for election to Congress.

The Bezos Day One Fund is named after the Amazon CEO's longstanding "Day 1" way of thinking. Bezos said he planned to use the charity to support homeless families and education programs in underserved communities.

The first round of donations, announced in November, went toward organizations fighting family homelessness. The fund's website hints at more donations to come, including some that will be used to launch "a network of high-quality, full-scholarship Montessori-inspired preschools in underserved communities."