Yet again, Harvard has been ranked as the No. 1 university in the world by the Academic Ranking of World Universities (ARWU). Harvard has held the top spot in the annual worldwide ranking since the list began in 2003.

The ranking was conducted by researchers at the Center for World-Class Universities of Shanghai Jiao Tong University and considers six objectives: the number of alumni and staff winning Nobel Prizes and Field Medals, the number of highly cited researchers selected by Thomson Reuters, the number of articles published in the journals of Nature and Science, the number of articles indexed in Science Citation Index Expanded and Social Sciences Citation Index and per capita performance of a university. Over 1,200 universities are ranked by ARWU, and the best 500 are published, according to the ARWU website.

Year after year, U.S. universities have topped the prestigious list. For the 2015 ranking, eight out of the top 10 best universities in the world are located in the U.S., and two were located in the United Kingdom.

There were only a handful of universities that ranked in the top 25 that were not from the U.S. or the United Kingdom, and those universities included the University of Tokyo, the Swiss Federal Institute of Technology, Zurich and the University of Toronto.

GettyImages-81463250 Graduating Harvard University students attend commencement ceremonies, June 5, 2008, in Cambridge, Massachusetts. Photo: Getty Images

The top 20 universities in the world for 2015, according to ARWU, are as follows:

1. Harvard University

2. Stanford University

 3. Massachusetts Institute of Technology

4. University of California, Berkley

5. University of Cambridge

6. Princeton University

7. California Institute of Technology

8. Columbia University

9. University of Chicago

10. University of Oxford

11. Yale University

12. University of California, Los Angeles

13. Cornell University

14. University of California, San Diego

15. University of Washington

16. John Hopkins University

17. University of Pennsylvania

18.University College of London

19. University of California, San Francisco

20. Swiss Federal Institute of Technology, Zurich