The Eigenfactor came out of the Metrics Eigenfactor Project, a bibliometric research project conducted by Professor Carl Bergstrom and his laboratory at University of Washington.

The Eigenfactor score measures the number of times articles from the journal published in the past five years have been cited in the JCR year.

Like the Impact Factor score, the Eigenfactor score is essentially a ratio of number of citations to total number of articles. However, unlike the Impact Factor, the Eigenfactor Score:

• counts citations to journals in both the sciences and social sciences
• eliminates self-citations.
• every reference from one article in a journal to another article from the same journal is discounted
• weights each reference according to a stochastic measure of the amount of time researchers spend reading the journal

Eigenfactor scores are scaled so that the sum of the Eigenfactor scores of all journals listed in Thomson's Journal Citation Reports (JCR) is 100. In 2015, the journal Nature has the highest Eigenfactor score, with a score of 1.992. The top thousand journals, as ranked by Eigenfactor score, all have Eigenfactor scores above 0.01.

Like the Impact Factor and Article Influence Score, the Eigenfactor Score uses Thomson Reuters (ISI Web of Knowledge) citation data to assess and track the influence of a journal in relation to other journals in the same discipline.

Eigenfactor Metrics are available only for JCR (Journal Citation Reports) years 1997 to 2015. 

The example below shows the top five journals using Eigenfactor in the JCR category of Astronomy & Astrophysics.