I've always heard that it was originally short for "Mind your Pints and Quarts!" Something an innkeeper (or what-have-you) would shout to an unruly...

It means Be on your best behaviour; be careful of your language. The date of the coinage of 'mind your Ps and Qs' is uncertain. There is a citation...

I read somewhere that it came about, ages ago, to remind people in the printing business, to be careful when typesetting 'p' and 'q', because it wa...

There are many theories, (some of them given in answers here) but none of them has any supporting evidence whatever. WorldWideWords has an article.

Anyone who has worked as a printer's devil knows the answer to the origin (and meaning) of the elderly term, "Mind your p's and q's." I must pref...

It's to do with the fact that children often confuse the small 'p' with the small 'q' when learning how to write and read (like they do with b's an...

Another theory I have heard - probably apocryphal - is that it has to do with the two branches of the Celtic family of languages: P-celtic (i.e. Br...

I've always understood as a warning to be polite. And I've always seen it this way: Mind your P's and Q's as in your "Pleases" (P's) and "Thank-you...