  Electron Multiplying CCDs (EMCCDs) are used much less often than they might
be because of the challenges they offer camera designers more comfortable with
the design of slow-scan detector systems. However they offer an entirely new
range of opportunities in astrophysical instrumentation. This paper will show
some of the exciting new results obtained with these remarkable devices and
talk about their potential in other areas of astrophysical application. We will
then describe how they may be operated to give the very best performance at the
lowest possible light levels. We will show that clock induced charge may be
reduced to negligible levels and that, with care, devices may be clocked at
significantly higher speeds than usually achieved. As an example of the
advantages offered by these detectors we will show how a multi-detector EMCCD
curvature wavefront sensor will revolutionise the sensitivity of adaptive
optics instruments and been able to deliver the highest resolution images ever
taken in the visible or the near infrared.
