What is the correct spelling and/or hyphenation for the abbreviation of electronic commerce?
I have seen the following variations.
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According to this Google Ngram, both E-Commerce and E-commerce are valid and interchangeable:
Likewise, when not beginning a sentence (or in a headline, etc.), the term e-commerce is not capitalized:
(noun) commercial transactions conducted electronically on the Internet.
See what happens when e-commerce is added to the Ngram.
According to Wikipedia, eCommerce is a viable, though less often used alternative. The Ngram supports that assertion. The only variation which is completely incorrect is ECommerce.
Definition from: New Oxford American Dictionary