  The $\bar{\nu}_{e}-e^{-}$ elastic scattering cross-section was measured with
a CsI(Tl) scintillating crystal array having a total mass of 187kg. The
detector was exposed to an average reactor $\bar{\nu}_{e}$ flux of
$\rm{6.4\times 10^{12} ~ cm^{-2}s^{-1}}$ at the Kuo-Sheng Nuclear Power
Station. The experimental design, conceptual merits, detector hardware, data
analysis and background understanding of the experiment are presented. Using
29882/7369 kg-days of Reactor ON/OFF data, the Standard Model(SM) electroweak
interaction was probed at the squared 4-momentum transfer range of $\rm{Q^2
\sim 3 \times 10^{-6} ~ GeV^2}$. The ratio of experimental to SM cross-sections
of $ \xi =[ 1.08 \pm 0.21(stat)\pm 0.16(sys)] $ was measured. Constraints on
the electroweak parameters $(g_V , g_A)$ were placed, corresponding to a weak
mixing angle measurement of $ \s2tw = 0.251 \pm 0.031({\it stat}) \pm
0.024({\it sys}) $. Destructive interference in the SM $\nuebar -$e process was
verified. Bounds on anomalous neutrino electromagnetic properties were placed:
neutrino magnetic moment at $\mu_{\nuebar}< 2.2 \times 10^{-10} \mu_{\rm B}$
and the neutrino charge radius at $-2.1 \times 10^{-32} ~{\rm cm^{2}} <
\nuchrad < 3.3 \times 10^{-32} ~{\rm cm^{2}}$, both at 90% confidence level.
