Since the start of the Snowden-revelations, we not only learned about the various collection programs and systems of the National Security Agency (NSA), but also about the various legal authorities under which the agency collects Signals Intelligence (SIGINT).
Bceause these rules are rather complex, the following overview will show which laws and regulations govern the operations of the NSA, showing what they are allowed to collect where and under which conditions. Also mentioned are various collection programs that run under these authorities.
The overview provides a general impression of the most important elements of the various laws and regulations and does not pretend to be complete in every detail. For example, provisions for emergency collection are not included. Also, some of these laws and regulations govern the work of other US intelligence agencies too, but here the focus is only on the NSA.