American Doctrine

I must confess that the word doctrine in conjunction with a name of an American president has always intrigued me. The mere sound of it has never failed to arouse my curiosity, raising in the process many disparate questions. How many doctrines are there? Do they have the same origin and definition? Alternatively, do they differ radically from one another? Who has the authority to proclaim a doctrine? Once declared, is it binding?
These and many other questions propelled me on a frantic search for the meaning and definition of that awesome word.