It would be easier to answer your question, if you were a little more descriptive.
The most common conspiracy theories include the assassination of JFK, the death of Elvis Presley, and 911.
Conspiracy is certainly interpreted in the common law. Many if not all States have statutes describing conspiracy, as well as the Model Penal Code defining it.
Boston Common - 1996 Conspiracy of Dunces 2-3 was released on: USA: 6 October 1996
The Apollo Moon landing hoax. While I agree with the above poster that the Moon Landing is quite a common theory, I would argue the Kennedy assassination is the most well known conspiracy theory.
Conspiracy
Yes, in most states.
V. A. Cheprakov has written: 'The Common Market conspiracy'
the dolphin conspiracy
Nothing. Conspiracy (to commit ANY crime) requires two or more persons colluding together. Murder can be commited by a single individual.
Conspiracy theories regarding aliens.
Yes. I was charged with conspiracy to sell a controlled substance in Lamar county in 2010 and it is most definitely a felony
Most people can't resist getting the details on the latest conspiracy theories, goal is to make the world safe for interdependence by protecting the benefits.