Encyclopedias contain factual articles on many subjects.

There are two types of encyclopedias -- general and subject. General encyclopedias provide overviews on a wide variety of topics. Subject encyclopedias contain entries focusing on one field of study.

• when looking for background information on a topic
• when trying to find key ideas, important dates, or concepts

• Encyclopedia of Major Marketing Campaigns (subject encyclopedia)
• Encyclopedia Americana (general encyclopedia)