In this thesis, aspects of mainly electric field effects on cellular systems are investigated, although electromagnetic effects on biological systems in general are also considered. The standard biotechnology processes of electroporation and electrofusion are shown to be electrically sub-optimal. Conventional d.c. pulses generate undesirable conditions such as asymmetrical membrane breakdown and cellular rotation. Normal electrical protocols also contribute to lower efficiencies by being sensitive to cell radii and other biological and physical variables. Both physical and numerical models indicated that replacing d.c. pulses with a.c. pulses symmetrical about a zero potential axis, not only reduces the inherent problems of asymmetrical breakdown and cellular rotation, but also provides the means to reduce efficiency sensitivity to cell radii. This is important in fields such as human monoclonal antibody research and the generation of transgenic animals. In addition, improvements to existing d.c. multiple pulse systems can be made by using shorter time constants and reducing the magnitude of successive pulse electric fields. The lysing effect of high magnitude electric fields are used in the study of disinfecting biologically contaminated liquids. It was earlier found that water could successfully be disinfected of the bacterial organism serratia marcescens. However, for higher liquid conductivities, applied electric field frequencies had to be increased so that electrolysis effects could be controlled. There is an upper limit to the frequency that can be used due to the cell membrane capacitance, which correspondingly puts an upper limit on the conductivity of the liquids that can be treated. Dead band regions where the applied a.c. electric field does not induce membrane dielectric breakdown, must be minimised. This suggests that a square wave should be used. Lower conductivity liquids are shown to provide the best opportunities for practical applications. Cancer cell growth modification unique to the combined effects of low magnitude d.c. electric fields and silver ions was found to exist. The morphological changes suggest that possible dedifferentiation of the cells has been achieved. Other metal ions tested did not produce the same results. Silver ion effects also provided evidence of disinfection properties that can be utilised in some water treatment applications. Resonant electromagnetic energy transfer into biological systems is investigated at a theoretical level. The resonant characteristic should enable specific targeting of effects which are related to the energy and power applied. Resonant characteristics of low level millimetre wave electromagnetic fields are suggested to be involved with cell to cell interactions. Thus, immunological function could be directly related to and altered by those fields. Higher energy effects are more likely to act by direct physical mechanisms and are therefore more likely to result in useful applications in the short term.