The Food and Drug Administration said it will not seek to regulate them under stricter rules for drug-delivery devices.
The news is considered a victory for makers and distributors of e-cigarettes, which continue to gain popularity worldwide.
E-cigarettes are plastic and metal devices that heat a liquid nicotine solution in a disposable cartridge, creating vapor that the "smoker" inhales. A tiny light on the tip even glows like a real cigarette.
Users say e-cigarettes use a nicotine vapor that gives them the sensation of smoking without the 4,000 chemicals found in traditional cigarettes.
First marketed overseas in 2002, e-cigarettes didn't become easily available in the U.S. until late 2006. Now, the industry has grown from the thousands of users in 2006 to several million worldwide, with tens of thousands new e-smokers every week.
No timeline was set for the proposed rule changes.
The Associated Press contributed to this report.