Avoid plastic bags and sealed containers when storing mushrooms as the lack of air flow will speed spoilage. Whole, raw mushrooms will keep from 4-7 days in the refrigerator, while sliced mushrooms (stored the same way), will last 1-2 days.
Do not wash until ready to use. To clean mushrooms, brush off any dirt and quickly rinse under water, then pat dry.
To freeze mushrooms, briefly steam or sautee, then allow them to cool before storing in a freezer-safe container. Make sure you label the container! They will keep their peak quality up to 10-12 months.