My favorite quote from this article:
As more internships sprouted across the country, Congress passed a number of laws regulating them, including the Fair Labor Standards Act of 1947, which specifically lays out a 6-point test, still in use today, for hiring unpaid interns. Under the Department of Labor’s test, an intern must be paid unless:
1. The internship is similar to training that would be given in an educational environment;
2. The internship is for the benefit of the intern;
3. The intern does not displace regular employees;
4. The employer derives no immediate advantage from the intern;
5. The intern is not entitled to a job at the end of the internship;and
6. The intern understands that he or she is not entitled to wages.