Environmental microbiological hygiene can be divided into two mainstreams: 1. Monitoring of microbiological strains, and, 2. Investigations on the circulation in the human and natural ecosystems by the micro-organisms. Increased understanding of the key role of environmental microbiology in the planetary survival strategy is a prerequisite for the transformation of human societies into sustainable economies. The book Microbiological Environmental Hygiene contains descriptions of the microbes and natural ecosystems from rain forests to arctic areas, as well as strains in the cleaning processes of human epithelia and food or water sources. It gives an insight into microbiological hygiene in various industrial effluents and focuses also on the prospects of environmental biotechnology, protection by natural and organic compounds, as well as against contamination or epidemics. This microbiological safety is monitored also in traffic systems and vessels. Different effects of climate change can be seen in the microbial ecosystems. It is essential to learn from the microbes and to develop the ecosystem services that allow humans to understand the ways they could be collaborated. This helps in cleaning up the soil, water and air. Also, the recalcitrant substances and plastics can get degraded by the microbes. Screening and source-tracking of water contaminations, as well as the promotion of soil fertility by microbes are presented. Both traditional microbiology and molecular methods are needed for the monitoring and research of the microbial agents. Microbiomes in the biosphere exercise interactions with other organisms, and they contribute to environmental health issues. Various groups of important micro-organisms are presented, such as environmental viruses and various bacteria, molds and yeasts, protozoa and algae. The utilization of biological organisms’ potential is studied for novel solutions. Microbiological Environmental Hygiene is the fourth part in a series on microbiological hygiene. This book combines the different fields of microbiology into a holistic view on the functions of the ecosystems and the cycles of matter, as well as the sustainable production of biochemical, fuels, gases and organic fertilizers with the help of microbes and their enzymes.