Which apartments are rent controlled?

Recently I've wondered why some apartments are rent controlled and others aren't. Intuitively, it seems like legislation should make it one way or the other. Tenants will always want rent control, while landlords will always want to get rid of it, so they can charge market rates. It turns out whether an apartment is rent controlled is generally determined by when it was constructed.

In the United States, rent control is handled on a state by state basis. In New York City, rent control applies to apartment built before 1947, but only if the apartment is passed down within a family since before 1971, and rent stabilization applies to apartments below a certain rent threshold built before 1974 with 6+ units. Other cities have taken different approaches. For example, in San Francisco only apartments constructed before 1979 are rent controlled.