Our recent experiments found evidence that answer the question, amazingly, in the affirmative. I will report on the observation of non-classical rotational inertia in solid He-4 confined to an annular channel in a sample cell under torsional motion, demonstrating sueprfluid behavior. Measurement of solid samples at different pressure (and hence different density) allows us to map out the phase boundary of this supersolid. These results indicate that superfluid behavior is found in all three phases of matter; gas, liquid and solid. This work is carried out in collaboration with Eunseong Kim and it is supported by the National Science Foundation of US.