  According to the inflationary scenario, all structure in the Universe can be
traced back to quantum fluctuations of the metric and scalar field(s) during
inflation. The seeds of this structure can be observed as classical
anisotropies in the cosmic microwave background. I briefly review how the
transition from the inherent quantum nature of these fluctuations to classical
behaviour comes about. Two features play a crucial role: Firstly, the quantum
state of the fluctuations becomes highly squeezed for wavelengths that exceed
the Hubble radius. Secondly, decoherence due to other fields distinguishes the
field-amplitude basis as the classical pointer basis. I also discuss the
entropy of the fluctuations and make a brief comparison with chaotic systems.
