Electro-optical effects are induced by external electric field pulses applied to solutions or suspensions and are recorded by various optical techniques. These effects are very useful for the characterization of macromolecular structures and their dynamics in solution. One of the field-induced effects is alignment of molecular dipoles, which can be detected at a very high sensitivity by measurements of the dichroism or the birefringence. Stationary values of these optical parameters recorded at different electric field strengths can be used to characterize dipole moments and to determine the orientation of chromophores with respect to the dipole vector. The transients reflect rotational diffusion, providing a particularly accurate measure of size and shape. The internal flexibility is also reflected in these transients. Another type of field-induced effect is chemical relaxation, which can be detected selectively and is very useful for the characterization of reactions, like ligand binding and conformation changes. The techniques based on electric field effects are unique in the sense that problems can be solved, which are difficult or even impossible to be sorted out by other techniques.