Microbiological industrial hygiene is defined as the safeguarding of industrial products, premises, personnel and raw materials from harmful or hazardous microbes which could cause a threat to the general public or the environment. The microbiological means for pursuing these goals in sampling, enrichment and detection are examined in the chapters of this book. Industries have been established for the production of a huge variety of products, from the cleanest medical or other healthcare products to the foods and other basic products people use on a daily basis. The micro-organisms are present in almost everything, and their presence needs to be monitored with skill. They often constitute an important component in the product composition by themselves. In these cases, the purity of the microbial supplements and seed cultures as well as their prevalence in the processes need to be surveilled. After this, the microbial communities could be within the scope of analysis. Sometimes, the industrial microbiomes need to be researched, too. Consequently, issues like clean room production, medical blood products, use of preservatives, milk and meat production, forest industry products, biorefineries, energy production with biohydrogen and methane, organic fertilisers and biochemicals are included in these chapters. Raw material safety, such as the Brucella spp.in milk is also dealt with in close attention. The microbiological industrial hygiene, as outlined above, should include the responsibility on the wastes of the various industries. In fact, these and the side streams could be converted into valuable raw materials for novel products with the aid of the microbes. This book introduces several steps for the industries to continue in this direction, which could also improve the overall hygienic status. The purpose of this book is to help the industrial production of microbiologically clean products using basic knowledge based on the microbiological and hygienic principles.