In practical terms:
* E-1 (Treaty Trader) visas are for people who work for companies that do a substantial amount of trade with the United States, and who will be working for that company in the United States for an extended period of time. E-1 visa applicants must establish to the satisfaction of the consular officer that their company carries on well-established and significant trade in goods and/or services between the treaty country (typically Mexico) and the United States.
* E-2 (Treaty Investor) visa are for people who personally invest a substantial amount of their own money in ventures within the United States. Typically, this means that they own companies in the United States that require substantial investment and that produce jobs for American citizens and/or legal permanent residents (outside their own family).