The purpose of this dissertation is to get some statistical results related to nontrivial zeros of L-functions. In the modular case, we prove and determine an explicit positive proportion of non-trivial zeros lying on the critical line. In order to obtain this result, we need to extend a theorem on shifted convolution sums on average to be able to determine the asymptotic behaviour of the mollified second integral moment of a modular L-function close to the critical line. Independently of these results, we study the smallest non-trivial zero in a family of L-functions. These results are applied to symmetric power L-functions.
