Studies conducted till now showed a favourable effect of magnetic field on the development of seeds and plants. The value of the effects obtained which are measured by the acceleration of seed germination and by a favourable effect on plant development and yield is different. This can be seen in their dependence on some physical factors – like the exposure dose and the kind of magnetic field applied, construction of the device used for seed stimulation, and also natural factors, like: plant species and variety, seed moisture content or course of the weather during vegetation. The problem of magnetic field effect on plant development and yield was, to a considerable degree, supported by many results, but general elucidation of this phenomenon requires further research, especially on the biochemical and physiological processes which occur in whole plants and in seeds. This problem will certainly be a subject of scientific interest, because according to some scientists problems from the borderland of biology and physics which require interdisciplinary actions will be among the most important research efforts undertaken in the present century. Explanation of their action mechanisms will be a great challenge for biophysics of the 21st century.