  We consider normalized analytic function $f$ on the open unit disk for which
either $\operatorname{Re} f(z)/g(z)>0$, $|f(z) /g(z) - 1|<1$ or
$\operatorname{Re} (1-z^2) f(z) /z>0$ for some analytic function $g$ with
$\operatorname{Re} (1-z^2) g(z) /z>0$. We have obtained the radii for these
functions to belong to various subclasses of starlike functions. The subclasses
considered include the classes of starlike functions of order $\alpha$,
lemniscate starlike functions and parabolic starlike functions.
