We discuss various properties of the Seiberg-Witten curve for the E-string
theory which we have obtained recently in hep-th/0203025.
Seiberg-Witten curve for the E-string describes the low-energy dynamics of a
six-dimensional (1,0) SUSY theory when compactified on R4R} X T2.
It has a manifest affine E8 global symmetry with modulus tau and
E8 Wilson line parameters mi, i = 1,2, ... ,8 which are
associated with the geometry of
the rational elliptic surface.
When the radii R5, R6 of the torus T2 degenerate
R5, R6 go to 0,
E-string curve is reduced
to the known Seiberg-Witten curves of
four- and five-dimensional gauge theories.
In this paper we first study the geometry of rational elliptic surface
and identify the geometrical significance of the Wilson line parameters.
By fine tuning these parameters we also study degenerations of our curve
corresponding to various unbroken symmetry groups.
We also find a new way of reduction to four-dimensional theories
without taking a degenerate limit
of T2 so that the SL(2, Z) symmetry is left intact.
By setting some of the Wilson line parameters to special values
we obtain the four-dimensional SU(2) Seiberg-Witten theory with
4 flavors and also a curve by Donagi and Witten describing the dynamics of
a perturbed N = 4 theory.