While bioprocesses using Escherichia coli, Corynebacterium glutamicum, various species of Bacillus, lactic acid bacteria, Clostridia, the yeasts Saccharomyces cerevisiae and Pichia pastoris, fungi such as Aspergillus niger, and Chinese hamster ovary cells are well established, the high level of microbial diversity has not yet been exploited industrially. However, the use of alternative organisms has the potential to significantly expand the process window of bioprocesses. These extensions include the use of alternative substrates (e.g., CO2, syngas, or methane), unusual process conditions (e.g., temperatures, media conditions), or use of microbial diversity itself (e.g., biofilm growth, alternative electron transport systems, product secretion, surface presentation of enzymes). Bringing these hidden champions into application will enable more efficient processes with environmental and ecological benefits. Some of the most promising alternative microorganisms are described and discussed in detail in this book. The aim of this introductory chapter is to provide an overview of additional organisms and cultivation strategies. Finally, it addresses future challenges to bring the organism into technical applications.