Photoirradiation and application of electric field give a powerful method to examine electronic structure of molecules and molecular systems and to control excitation dynamics, material function and biological function. Electric dipole moment in the excited state as well as in the ground state of molecules and molecular systems can be determined using Stark quantum beat spectroscopy in vapor phase and using electroabsorption (E-A) and electrophotoluminescence (E-PL) spectroscopy in condensed phase. Electric field effects on photoexcitation dynamics in organic photoinduced electron transfer systems, π-conjugated polymers and semiconductor quantum dots, which play an important role in optoelectronic devices, have been elucidated, based on the measurements both of the E-A and E-PL spectra and of the field-induced change in emission decay profile. Electrical conductivity in organic conductors can be controlled by photoirradiation and application of pulsed electric field, that is, tuning of electrical conductivity among insulator, metal and superconductor is possible with photoirradiation and application of electric field. Intracellular function is affected by application of short-pulsed electric field, that is, electric-field-induced apoptosis has been confirmed. It is also proposed that fluorescence lifetime microscopy is applicable to evaluate the local electric field in cells, which seems to be one of the vital factors that control the reactions in biological systems.