Spar has written about the economics of the human fertility industry and the evolution of the Internet.[5] Her work on the economics of fertility drew wide attention.[6]
She has appeared on 60 Minutes, The News Hour with Jim Lehrer, ABC World News Tonight, and in many newspapers and magazines. Her own articles have appeared in publications ranging from The New England Journal of Medicine to Foreign Affairs to The Review of International Political Economy.[7]
In 2001, she wrote an article called "Why the Internet Doesn't Change Everything" which described the distinctive nature of the internet industry. Her book, The Baby Business: How Money, Science and Politics Drive the Commerce of Conception, pioneered research about the economy of alternative fertility. Spar was the first academic to mention fertility as a transaction through a business framework. In various interviews online, Spar said that when she picked up the research topic of fertility through an economic lens, her colleagues did not take her seriously and called her soft. She followed up in 2006 with a book named The Hidden Market for Babies. Spar has also written about AIDS, African economics, the global economy, the balance of power, and terrorism.
A leading figure in business academics, Spar also ran Making Markets Work, joint program between Harvard Business School and the University of Pretoria Gordon Institute of Business Science. The course in South Africa teaches about the interconnection of the public and private sectors' effects on economic growth. Spar also spearheaded the initiative in Rwanda, where cabinet members learned about executive education.
During her inaugural address on October 23, 2008, Spar cited a number of goals for her term as President of Barnard College. Paramount were her desire to make Barnard a more internationally recognized institution for women, as well as expand and improve the current Barnard Leadership Initiative (BLI). She followed up on this goal by converting BLI into Barnard's Athena Center for Leadership Studies.[8]
Spar also served as a member of the Board of Directors of American investment bank Goldman Sachs from June 2011 to April 2017.[9]