One or both of these abbreviations usually precede opinions about law. The use of these abbreviations serves as a warning for the reader not to take the opinion as professional legal advice. Many jurisdictions have legal restrictions on actually giving or even appearing to give legal advice, or otherwise practicing as a lawyer without legal qualifications and official registration. Rendition of legal advice by a person who is not licensed to do so can be the basis for a charge of Unauthorized practice of law.
The expression is one of "the most popular" internet acronyms. The origin of the term is in a 1980s commercial for Vicks Formula 44 cough syrup, in which two spokesmen successively pitched the over-the-counter medication with the line, "I'm not a doctor, but I play one on TV." The spokesmen were soap opera actors Chris Robinson (who played Dr. Rick Webber on General Hospital) and Peter Bergman (who played Dr. Cliff Warner on All My Children). The transfer from doctor to lawyer is an example of a snowclone. The term IANAL is reported to have been "common on Usenet by the late '80s and early '90s.
A variant of IANAL is IANYL ("I am not your lawyer"). The term may be used by a lawyer posting comments on a message board to indicate that the commentator is, in fact, a lawyer, but to emphasize that the commentator does not represent the reader, and to indicate that the comments are neither protected by attorney-client privilege, nor may be the basis for a malpractice lawsuit should the suggestion be followed with undesirable results. IAAL ("I am a lawyer") is sometimes used as well, usually with an explicit disclaimer such as "IAAL, but I'm not your lawyer".
The case law standard for determining what comments cross the line is generally "the application of law to facts specific to an individual seeking legal advice". Attorneys may use a disclaimer to reduce confusion, and "I am not your lawyer" is part of a typical disclaimer. There are "weighty obligations" that go along with the creation of a lawyer-client relationship, particularly if an "online exchange includes legal advice relating to the client's specific facts". Courts have held that (in the case of 900 numbers) boilerplate disclaimers without clear actions to indicate assent may not avoid the creation of a lawyer-client relationship.
Other variations of IANAL refer to different fields, such as IANAMD for "I am not a Medical Doctor." These serve the same general purpose as IANAL — to discourage the use of the information as actual professional advice.
A Christian variation is IANACL, meaning "I am not a canon lawyer."