From it's needle like leaves and strong resinous aroma you'd almost think this was some sort of conifer, but no, it's yet another mint. This is a very powerful herb to be used with discretion, fresh or dried. Fresh is considered superior for all uses, and it's the easiest herb there is to have fresh - it grows eagerly under poor conditions and can even get out of control. Various rosemary cultivars are used as durable, almost indestructable hedges, groundcovers and decoratives here in Southern California - and it even grows well in England!
Rosemary has an affinity for meats, poultry and some vegetables when fried in olive oil, particularly potatoes but also eggplant, zucchini and tomatoes. It also has medicinal properties and is thought to help protect the brain from free radicals and possibly improve memory. It is very safe in culinary and theraputic doses but is toxic in very large amounts (how you could eat that much of it I haven't a clue) and rosemary oil or extract must be used carefully. Photo © cg1.
More on Mints.
Buying: Well, if you really must buy it, you'll find fresh rosemary in the the herb section of just about any modern supermarket, and at just about any farmer's market where any herbs are sold. I humbly suggest growing you own, or snatching a frond from somebody's landscaping (you don't need much - its strong).
Dried is available in the spice section of most supermarkets. Buy only whole leaf, never powdered. To substitute dry for fresh, or vice versa, the quantity should be roughly the same.
Storing: Loosely wrapped, it should survive a couple of weeks in the fridge. I'm not really sure because I just go outside and cut some when I need it.
Cooking: Use descretion, generally don't use more than the recipe calls for. Rosemary can withstand rather long cooking without fading so it usually goes in early.