During the past few years we have seen an impressive number of studies using directed self-assembly in soft matter research with a surprisingly wide range of underlying aims and goals. Here we will focus on field-driven colloidal self-assembly, and demonstrate how we can apply external electromagnetic fields in order to modulate the intrinsic interparticle interactions and induce additional directional ones in order to tune the subtle balance between thermal motion and the action of interparticle forces and thus generate new self-assembled structures. We describe two interesting classes of responsive particles, ionic microgels and hematite core-shell colloids, and use various real and reciprocal space techniques to monitor the particles in situ and time resolved while they assemble into the targeted structures. We show in particular how we can use field-driven self-assembly to induce phase transitions, cycle through various equilibrium and non-equilibrium phases, and study the underlying mechanisms of these phase transitions. Moreover, we demonstrate the effect of particle anisotropy in field-driven assembly.