  In this set of four lectures I will discuss some aspects of the Standard
Model (SM) as a quantum field theory and related phenomenological observations
which have played a crucial role in establishing the $SU(2)_{L} \times
U(1)_{Y}$ gauge theory as the correct description of Electro-Weak (EW)
interactions. I will first describe in brief the idea of EW unification as well
as basic aspects of the Higgs mechanism of spontaneous symmetry breaking. After
this I will discuss anomaly cancellation, custodial symmetry and implications
of the high energy behavior of scattering amplitudes for the particle spectrum
of the EW theory. This will be followed up by a discussion of the 'indirect'
constraints on the SM particle masses such as $M_{c}, M_{t}$ and $M_{h}$ from
various precision EW measurements. I will end by discussing the theoretical
limits on $M_{h}$ and implications of the observed Higgs mass for the SM and
beyond.
