  The transition from galactic to extragalactic cosmic rays is discussed. One
of critical indications for transition is given by the Standard Model of
Galactic cosmic rays, according to which the maximum energy of acceleration for
iron nuclei is of order of $E_{\rm Fe}^{\rm max} \approx 1\times 10^{17}$ eV.
At $E > E_{\rm Fe}^{\rm max}$ the spectrum is predicted to be very steep and
thus the Standard Model favours the transition at energy not much higher than
$E_{\rm Fe}^{\rm max}$. As observations are concerned there are two signatures
of transition: change of energy spectra and elongation rate (depth of shower
maximum in the atmosphere $X_{\rm max}$ as function of energy). Three models of
transition are discussed: dip-based model, mixed composition model and ankle
model. In the latter model the transition occurs at the observed spectral
feature, ankle, which starts at $E_a \approx 1\times 10^{19}$ eV and is
characterised by change of mass compostion from galactic iron to extragalactic
protons. In the dip model the transition occures at the second knee observed at
energy $(4 -8)\times 10^{17}$ eV and is characterised by change of mass
composition from galactic iron to extragalactic protons. The mixed composition
model describes transition at $E \sim 3\times 10^{18}$ eV with mass composition
changing from galactic iron to extragactic mixed composition of different
nuclei. These models are confronted with observational data on spectra and
elongation rates from different experiments, including Auger.
