  The nature of CME-associated low corona propagating disturbances,
  'EUV waves', has been controversial since their discovery by EIT on
  \textit{SOHO}. The low cadence, single viewpoint EUV images and the lack of
simultaneous inner corona white light observations has hindered the resolution
of the debate on whether they are true waves or just projections of the
expanding CME. The operation of the twin EUV imagers and inner corona
coronagraphs aboard \textsl{STEREO} has improved the situation dramatically.
During early 2009, the \textsl{STEREO} Ahead (STA) and Behind (STB) spacecraft
observed the Sun in quadrature having an $\approx 90^\circ$ angular separation.
An EUV wave and CME erupted from active region 11012, on February 13, when the
region was exactly at the limb for STA and hence at disk center for STB. The
\textit{STEREO} observations capture the development of a CME and its
accompanying EUV wave not only with high cadence but also in quadrature. The
resulting unprecentented dataset allowed us to separate the CME structures from
the EUV wave signatures and to determine without doubt the true nature of the
wave. It is a fast-mode MHD wave after all!
