Wash green and wax beans; drain. Trim ends and break or cut into 1-inch pieces; measure 12 cups of beans. Wash and drain Italian beans. Measure 4 cups. Place in an 8- or 10-quart Dutch oven or kettle.
Add enough boiling water (about 10 cups) to cover beans; return to boiling. Boil, uncovered, for 5 minutes.
Using a slotted spoon, pack hot beans into hot, clean pint canning jars, leaving 1/2-inch headspace. If desired, add 1/4 to 1/2 teaspoon salt to each jar. Add boiling water, leaving 1/2-inch headspace. Remove air bubbles, wipe jar rims, and adjust lids. Process filled jars in a pressure canner, at 10 pounds pressure for weighted canners or 11 pounds for dial-gauge canners, for 20 minutes. Allow pressure to come down naturally. Remove jars from canner; cool on racks.