What is the difference between the org.junit package and the junit.framework package?

What is the difference between the org.junit package and the
junit.framework package?

Whenever I use a Junit assert in my code, my IDE (Intellij IDEA 12)
politely offers to static-import it for me:
import static junit.framework.Assert.assertTrue;
However, it always gives me the choice of importing either the "org.junit"
version or the "junit.framework" version:
import static org.junit.Assert.assertTrue;
I can't find a clear answer online about what the difference is between
these two packages - is there a difference? If so, what is it? They both
come out of exactly the same Junit4 jar, so what's going on?