This Thesis, containing the main results of my PhD studies during the period January 2007-December 2009, deals with the analysis of the dynamical behavior of complex spin systems. In particular the attention is focused on the so-called central spin models, describing the interaction of one or few spins with an environment of uncoupled spins, as well as on a system consisting of two interacting spins coupled to a bosonic bath. Generally speaking the dynamics of real systems deviates from the Markov evolution especially when spin baths are considered. The analysis we have done is developed in the framework of non-Markovian master equations and allowed us not only to derive the dynamical properties of the system under scrutiny but also to test the validity of approximate techniques generally exploited for a systematic description of non-Markovian features in the dynamics of open systems.