Monday's Los Angeles Times takes an in-depth look at hemp in The Demonized Seed (free subscription required):

As a Recreational Drug, Industrial Hemp Packs the Same Wallop as Zucchini. Why Does the U.S. Drug Enforcement Agency Continue to Deny America This Potent Resource? Call It Reefer Madness.

The facts:

Because they're often used interchangeably, the terms cannabis, hemp and marijuana can be confusing. While cannabis encompasses all varieties of the species, hemp, often called industrial hemp, has come to mean a few dozen nonintoxicating varieties of cannabis bred and cultivated for commercial ends: clothing, paper, food, biofuels, biodegradable plastic, building materials, automobile parts, insulators, paints, lubricants—the list of possibilities goes on.

Marijuana, on the other hand, refers strictly to the cannabis drug plant, of which there exist endless varieties differentiated by the amount of intoxicating substances they contain, notably tetrahydrocannabinol (THC). Today virtually all strains of cannabis are the product of human alteration, manipulated by scientists, breeders and drug dealers to increase or decrease THC content and other characteristics to suit their purposes.