The coupling of fast and Alfven magnetohydrodynamic (MHD) waves is of fundamental interest in astrophysical plasmas. Under certain conditions, Alfven waves can be resonantly excited by fast mode waves, resulting in a localised accumulation of energy in the plasma. In the solar community this is often referred to as resonant absorption, while in the magnetospheric community it's known as field line resonance. These processes have applications in coronal heating and in magnetospheric dynamics.Alfven resonances are well understood in 1D and 2D, but not so in 3D, particularly in non-Cartesian geometries. We present a theoretical way of understanding the structure and temporal development of Alfven resonances in 3D, which is corroborated by numerical simulations. [mehr]