The thesis studies the integer-power moments of the central values of
families of modular L-functions. The two families under consideration in
the thesis are those quadratic twists of a L-function associated with a
cusp from and L-functions of a Hecke-basis of the space of cusp forms.
Applications of the moment estimates derived in the thesis include (1) a
non-vanishing result (2) a zero density estimate for quadratic twisted
L-functions.