How do I find journal impact factors and related citation data for journals?

This information is found in a database called Journal Citation Reports (JCR). Data on science and social science journals is available back to 1998.

Once you are in the database, you can choose to search for a specific journal or for a set of journals within a discipline or publisher. For any given journal, you can see the number of citations to the journal in the data year (e.g., 2005), the Impact Factor and other clever measures like cited half-life.

Click on the Category link from any individual journal's data and then sort that list by Impact Factor. You can see where a specific journal ranks out of all journals in a given category.