Several types of bay leaves exist and not all of them are safe to eat. For instance, the mountain laurel is a type of bay plant that is toxic to livestock; leaves from the laurel cherry tree are dangerous for humans to eat. Bay laurel (Laurus nobilis) is the type of bay leaf that is often included in soups, stews and other slow-cooking dishes.
Bay laurel is indigenous to the Mediterranean, but also thrives well in other parts of the world with a similar climate. The plant has been cultivated since the 1600s in other countries besides those in the Mediterranean region, "making it one of the oldest cultivated plants," according to the University of Illinois. California bay leaves are grown in the U.S. as well and have a more savory taste than the sweeter Mediterranean laurel.
If you're using whole bay leaves for cooking, it's best to remove the leaves after the food has finished cooking, since the texture makes the bay leaves hard to chew and digest. However, the bay leaves are edible in powdered or crushed form and don't have to be removed from cooked dishes.