Transport through a metallic nanoparticle is governed by Coulomb blockade physics. Due to the discrete character of the charge the current is suppressed up to a finite threshold voltage. The current is a strongly non-linear function of bias voltage, which includes a staircase behavior under certain circumstances. When the nanoparticle is placed in between two ferromagnetic electrodes the interplay of ferromagnetism and discrete charging leads to new phenomena. If the nanoparticle is metallic and the spin relaxation time in it is long, a spin dependent potential in the nanoparticle, the so-called spin accumulation, can appear. Charging effects are strongly enhanced in nanoparticle arrays . In this talk, after an introduction to Coulomb blockade physics and spin accumulation I will show that the interplay between ferromagnetism and charging effects has a very strong effect in the transport properties of nanoparticle arrays, resulting in very unusual current-voltage and magnetoresistance curves.