The main result of this dissertation is an asymptotic formula for the fourth moment of automorphic $L$-functions of prime power level [rho vu], [vu] --> [infinity]..  This is a continuation of the work of Rouymi, who computed the first three moments at prime power level, and a generalisation of results obtained for prime level by Duke, Friedlander & Iwaniec and Kowalski, Michel & Vanderkam.