Molecular magnets are a class of magneto-organic material which behave at low temperatures like a single quantum spin of large angular momentum. In this thesis we will be concerned with the spin dynamics of these molecular magnets, occurring both in isolation, and in contact with external environments and with other molecular magnets. We begin by addressing the possibility of non-Abelian adiabatic transport in molecules of half-integer spin, under slow rotations of the molecule. Next we analyze the process of dissipative spin tunneling for a single molecule interacting with a phonon bath. Finally we attend to the problem of collective magnetization in a lattice of spins coupled by dipole-dipole interactions.