Despite many efforts to uncover the mechanism of supersolidity since the first observation of non-classical rotational inertia in solid helium in 2004 [1], the microscopic origin and physical interpretation of the observed phenomena are still a subject of considerable intrigue. In this talk, I will review and correlate recent experimental results to provide an up-to-date picture of what we do and still do not understand. I will also take the opportunity to highlight the recent progress in solid helium experiment under rotation.

1. E. Kim and M. H. W. Chan, Nature 427, 225 (2004)