What is Castile Soap?

According to Janice Cox, author of Natural Beauty at Home...More Than 250 Easy to Use Recipes for Body, Bath and Hair, Castile soap is a mild white soap made with olive oil. It is named after the Castile region in Spain where it was developed. Real castile soap must be made with 40% olive oil. It can be purchased at many grocery stores (like Trader Joe's) and natural food stores in both bar and liquid forms.