The pion form factor has been measured in a rather wide range of
-values as shown in Fig.(2). The time-like region,
, has been
accurately explored by various 
-machines not only in the
interesting region around the 
resonances, where
and 
are large, but also at
much higher 
-values. Experimental details and references can be
seen in the reviews by Bauer et al [1] and Dolinsky et al
[2].
The reaction 
(inverse electroproduction),
on the other hand,
allows to cover the lower 
-region just above 
.
For 
-values in the space-like region,
good data are also available (most of them from elastic 
scattering, but also from the (
-electroproduction) reaction 
; see ref. [3], for details). Some of them are
also shown in Fig.(2).
Figure 2: A plot of the pion form factor versus energy as determined
from colliding beams, inverse electroproduction and electroproduction
measurements. Details and fits can be found in
ref.[1]
All the gross features of these data are approximately explained by a
simple 
-meson Breit-Wigner dominating this pion form factor.
This reasonable simple-pole description clearly suggests and
illustrates the success of naive vector-meson dominance models (VMD).
Interesting modifications to this simple one-pole behaviour have been
detected around the 
and 
peaks, showing again the
relevance of vector-mesons even in isospin violating channels. Other
structures seem to be present at higher energies as discussed in ref.
[4]. At asymptotic energies, the Brodsky-Farrar quark counting
rules, derived from QCD, predict the simple pole dependence 
[5].
From the well measured behaviour around 
, the pion charge
radius can be defined. We quote the value
coming essentially from ref.[6] but coinciding with several
independent measurements and their global mean value [7]
with one exception: that coming from old data [8] on 
and leading to 
.
As far as Daphne is concerned, a high precision measurement of the pion
form factor near the threshold, as well as in the region around
the 
-meson, is crucial for reducing the theoretical error in
the hadronic contribution to the muon anomalous magnetic moment (see
Franzini's contribution to this chapter).
Similarly, Daphne offers exceptional opportunities to improve the
measurements of 
around the 
-peak. This is
essential to understand the 
contaminations in the
mainly 
-meson wave function.
