Meiobenthology is the science of the tiny animals that live in huge numbers in all aquatic sediments. This fully revised and enlarged second edition emphasizes new discoveries and developments in this field. Major progress has been made in three general areas: - Systematics, diversity and distribution, - Ecology, food webs, and energy flow, - Environmental aspects, including studies of anthropogenic impacts. The meiobenthos of polar and tropical regions, deep-sea bottoms and hydrothermal vents are now studied in more detail. The high number of species found to survive under such extreme conditions puts them at the forefront of biodiversity studies. Molecular screening methods enable large numbers to be analyzed upon applying reasonable effort. The aim of this book is to synthesize these modern scientific achievements such that meiobenthology can play a key role in aquatic research and in assessing the health of our environment.