My dog is losing a lot of hair

What breed/mix is she?
How old is she?
Is she an indoor dog or outdoor dog?
Was she a primarily outdoor dog who is now being kept indoors?
Is your part of the world going into Springtime?
Have you moved to a warmer climate?
How does her skin look?
Is the shedding in one area or all over?
Any other symptoms? Any changes in eating, drinking, playing, etc.
Any changes in her environment or stress level?