Fungi are dominant microorganisms in all terrestrial ecosystems. They are major saprophytes, they are very important pathogens, and they are key symbionts. The ecology of the fungi is thus of essential importance for the functioning of the whole ecosystem. In this contribution some very general aspects of fungal ecology will be shortly addressed with special emphasis on terrestrial, non-pathogenic fungi. In particular, fungal succession will be discussed, that is how different fungal species or groups of species or physiological groups follow each other in different substrata. When considering introduction of new fungi into an environment, be these genetically modified or not, knowledge on the successional patterns of the fungal community existing in the ecosystem in question is important for increasing the chances of a successful introduction. Some aspects on disturbance effects on the fungal community and function of the community of disturbances will also be considered. One example of a disturbance is the introduction of a new species, clearly illustrating the relevance of disturbance studies. For better understanding both successional and disturbance aspects of fungal ecology, some different life strategies of fungi will be referred to. More comprehensive presentations of these aspects of fungal ecology are given by e.g. Cooke and Rayner (1984), Frankland (1981, 1992), Zak (1992).