Bulk herbs. This is the plant at its most natural (unless you count the way it was when it was still growing). Bulk, or crude, herbs are the medicinal or therapeutic parts of a plant that have been harvested and separated from the nontherapeutic parts.

Powdered herbs. These herbs have been dried and ground up. They can be used to make teas, poured into capsules, or taken straight.

Teas: Infusions and decoctions. A tea or decoction is made by drawing the herb's constituents — its pigments, essential oils, nutrients, and phytochemicals — into water, which acts as a solvent to dissolve the plant matter (a tea is steeped, a decoction is boiled). Leaves and flowers are generally made into infusions, and roots and bark are made into decoctions.

Tinctures. A tincture is an herbal extraction that uses a chemical solution (most often alcohol) as the solvent. Tinctures are stronger than crude or powdered herbs and teas/decoctions, and are easy to take (they're also readily absorbed into your bloodstream).

Extracts. Herbal extracts are sold as liquids or solids (capsules or tablets) and are also easy to use.

Essential oils. These are highly concentrated oils — not thick or greasy, but watery and volatile. Essential oils are plant extracts that contain only the “essential” ingredients: the plant's phytochemicals and its fragrance. Used in aromatherapy, essential oils are either inhaled or applied directly to the skin (usually after being diluted in a carrier oil, such as almond or sesame oil). They're also incorporated into topical herbal treatments such as lotions and creams.

Topical treatments. These include ointments (salves), gels, lotions, infused oils, and creams, and can contain wildly varying amounts of herbs. Some have a medicinal or therapeutic dose of something — enough calendula (Calendula officinalis ) to relieve your rash, for example — while others have just enough to make the product smell nice.