Self-rising flour is a modern American convenience, utilized by the resourceful housewife to more quickly make biscuits and batter breads. In this age of electric stoves and microwaves, most groceries have stopped selling self-rising flour in favor of additional shelf space for boxes of pasteurized curry-tomato soup.1

Basically, self-rising flour is a medium-strength wheat flour with chemical leavening. For those of us who do not keep it on hand, it can be quickly mixed from its components:2

1. Occasionally I do find boxes of self-rising cake flour on the grocery store shelves. While the softer cake flour does make excellent biscuits, generally I avoid buying it, as baking powder does lose strength as it ages, and those boxes seem ancient.
2. One might notice that mixing these ingredients is the very first step given in blaaf's excellent recipe for baking powder biscuits.
3. For those of you who might want to transform an entire five pound bag of flour into self-rising flour, you'll want to use 1/2 cup baking powder and 1/4 cup salt. Make sure you sift well.