Amateur Radio Regulations
In the United States and other areas under the jurisdiction of the FCC, the rules for amateur radio operation are contained in Part 97 of Title 47 - Telecommunications, of the United States Code of Federal Regulations (CFR). Specific paragraphs within these rules are often abbreviated as, for example, "47CFR97.303(a)".
The most up to date version of the amateur radio regulations is available at this Electronic Code of Federal Regulations web site, operated by the federal Government Publishing Office.
You are encouraged to download, read and keep available this PDF version of the rules, maintained by the ARRL.
All hams are required to be familiar, and comply, with the entire Part 97. However, some sections of the regulations are listed and linked below for easy reference, as they contain material a ham may want to refer to on a repeated basis.
47CFR97.301 - Authorized frequency bands.
This section lists all the frequencies hams can use, divided by license class: Novice, Technician, General, Advanced and Amateur Extra. It includes references to any restrictions given in specific paragraphs of 47CFR97.303.
47CFR97.303 - Frequency sharing requirements.
This section contains any restrictions that apply to a given frequency segment, including whether it is primary or secondary for amateur use.
47CFR97.305 - Authorized emission types.
This section describes the types of emission (phone, CW, data, etc.) that may be transmitted on each frequency segment.
47CFR97.405 - Station in distress.
Contrary to what you may hear from many people, including a number of hams, you may NOT "do whatever it takes" just because there has been a disaster or other emergency that you are helping to recover from. You may not use non-ham frequencies, exceed power limits or violate any FCC regulations in this situation. The above two paragraphs clearly state that an amateur station may use "any means of radiocommunication at its disposal" ONLY when both of these two conditions apply:
a.) when the station operator itself, or another person it is assisting, is in distress, and
b.) when "normal communication systems are not available."
Note: The FCC explains in Part 80-Maritime Services (47CFR80.5 - Definitions) that a distress signal "indicates that a person, ship, aircraft, or other vehicle is threatened by grave and imminent danger and requests immediate assistance".