This paper provides a brief introduction to the impact factor (IF), a number that judges the importance of a scientific/engineering journal. Using a simple equation, the IF can be determined and used to indicate the importance of a journal. While a correlation exists between the journal IF and the quality of the journal, comparing IF between two disciplines may not be fair. Nevertheless, the IF is gaining popularity among college presidents who are determined to improve their school's status in the US News and World Report college rankings.