Cultivated Common Field Mushrooms come in three sizes, the most common being the smallest or Button Mushroom. They are creamy white, with caps tightly closed. Mushrooms are in the same family as yeasts and mold. They have been consumed for thousands of years, and are considered a delicacy. They appeared in the Ancient Egyptian Hieroglyphics as food for the Pharaohs. In Greece and Rome, they were reserved for the upper class.
In modern times, it was the French that cultivated mushrooms on a commercial basis. By 1920, commercial mushroom production came to the United States and today, Pennsylvania produces over half of all of the Button mushrooms sold. Commercial Button mushrooms are low in sodium, and high in potassium, and are low in calories, and good for heart smart eating. One cup has only 20 calories. 

For all types of mushrooms, look for clean caps, free from blemishes, slimy spots or signs of decay. Allow for 1/4 to 1/2 pound per person per serving when used as a vegetable.

Store mushrooms, unwashed in a plastic or paper bags. Keep away from strawberries, and other vegetables in the produce refrigerator, as the spores can hasten the destruction of these fruits and vegetables.

Wipe with a damp cloth before use. Do not soak mushrooms.

Mushrooms can be steamed, broiled, baked, fried, or grilled.

Here is a great resource for all things mushroom:
http://www.mushroomcouncil.com/