Guybrush,
There are tonloads of rules, CAA, FAA, whicheverAA, - the thing is, there is not much enforcement unless some poor tired pilot cocks up.
ICAO has many guidelines that countries can opt into or out of, piecemeal if they want. Many countries register exceptions.
IATA is an airline association that tends to be involved more in fares and ticketing and the like.