Extreme environments - from glaciers and deserts to hypersaline waters, acidic brines, and oligotrophic rocks - appear profoundly different, yet many are united by a common physicochemical constraint: low water activity. Far from being aseptic, these habitats support diverse microbial communities in which extremophilic and extremotolerant fungi play fundamental ecological roles. Once regarded as rare or incidental, these fungi are now recognized as key components of extreme ecosystems, capable of surviving, thriving, and evolving under conditions that are lethal to most life forms.
This volume presents a comprehensive overview of the diversity, biology, evolution, genomics, stress adaptation, and biotechnological potential of extremophilic fungi. It examines both habitat specialists and remarkably versatile extremotolerant generalists, revealing the molecular and physiological strategies that allow them to cope with multiple environmental stresses. The chapters follow these fungi across both natural and human-made environments - from glaciers, hypersaline waters, deserts, and oligotrophic rocks to indoor appliances, cultural heritage materials, and other habitats of the technosphere. In doing so, they reveal common adaptive principles that transcend individual ecosystems while exploring fungal biodiversity, model organisms, microbial interactions, and emerging applications in agriculture, bioremediation, and sustainable biotechnology. 
Extremophilic fungi are more than organisms that endure harsh conditions. Their extraordinary metabolic plasticity and evolutionary versatility provide unique opportunities to understand the limits of eukaryotic life while inspiring innovative biotechnological solutions. By viewing seemingly disparate habitats through the common lens of low water activity, this volume offers a new framework for understanding fungal adaptation across the natural world.
Written by leading researchers in the field, this volume provides an authoritative synthesis of one of the fastest-growing areas of modern mycology. It is an essential resource for mycologists, microbiologists, ecologists, molecular biologists, evolutionary biologists, and biotechnologists interested in life at its environmental limits.

Nina Gunde-Cimerman is Professor of Microbiology at the University of Ljubljana, Slovenia, where she leads the research group Biology of Microorganisms. She received her PhD (1993) from the University of Ljubljana.
Her research focuses on the diversity, ecology and adaptation of extremophilic and extremotolerant fungi, particularly those inhabiting environments with low water activity. In 2000, her group reported halophilic fungi on the Slovenian Adriatic coast, followed by studies of fungi from Arctic subglacial ice. These findings led to broader investigations of fungal life in extreme habitats, ranging from hypersaline environments, glaciers and deserts to human-made extreme environments such as household dishwashers.
Her current work addresses fungal polyextremotolerance and the mechanisms enabling fungi to tolerate combinations of environmental stresses. Particular attention is given to fungi adapted to high concentrations of NaCl and chaotropic salts, including MgCl₂ and LiCl, and to fungal diversity in poorly explored environments such as high-altitude lakes of the Bolivian Altiplano and acidic volcanic habitats in Mexico. Her research combines biodiversity studies, phylogenetics and phylogenomics, comparative and population genomics, transcriptomics and experimental approaches to fungal stress adaptation.
Her group maintains the EX Culture Collection of extremophilic and extremotolerant fungi, comprising more than 19,000 strains from natural and human-made environments and an expanding collection of sequenced fungal genomes. These resources support research ranging from fundamental studies of fungal adaptation to applications in biotechnology, bioremediation, sustainable agriculture and environmental and health-related research.
Gunde-Cimerman has coordinated and participated in numerous national and international research projects and collaborations. She has also organised international scientific meetings on halophiles, polar, polyextremophilic microorganisms and black fungi, and in 2023 chaired the first international FUN-EX meeting dedicated to extremophilic fungi.
She is an ISME ambassador,  member of EMBO and a Fellow of the European Academy of Microbiology. She is also actively engaged in science communication through public lectures and the media.
Polona Zalar is an Assistant Professor of Microbiology at the University of Ljubljana, Slovenia, where she teaches courses in general microbiology and mycology. She leads the Molecular Biology of Microorganisms research program and has been actively engaged in fungal taxonomy and ecology throughout her career.
She earned her B.Sc. in 1995, M.Sc. in 1999, and Ph.D. in 2006, all from the University of Ljubljana. Her expertise in fungal taxonomy was further deepened through specialized training at the IMI–International Mycological Institute in Egham, UK (now CABI UK Centre), the CBS–Centraalbureau voor Schimmelcultures in Utrecht, the Netherlands (now Westerdijk Fungal Biodiversity Institute), and through mentorship by renowned mycologists Prof. Hennebert and Prof. de Hoog.
Dr. Zalar has authored numerous research articles, with a particular focus on the discovery and classification of novel fungal taxa from extreme environments, such as natural saline habitats and Arctic subglacial ecosystems. Her current research emphasizes xerophilic fungi, especially those involved in the biodeterioration of cultural heritage. In this area, she has led two national research projects addressing mold contamination in museum collections and has contributed to numerous additional initiatives exploring fungal biodiversity.