Fungi are cryptic, understudied and hyperdiverse organisms. In this chapter I address the wonders of fungal diversity, including recent advances on the understanding of the evolution of the kingdom Fungi, approaches to documenting and interpreting fungal diversity, and current efforts concerning fungal conservation. Fungi are eukaryotic organisms that cannot produce their own energy and depend on enzymatic processes to break down biopolymers that are then absorbed for nutrition. The kingdom Fungi encompasses tremendous biological diversity, with members spanning a wide array of lifestyles, forms, habitats, and sizes. Fungi are sister to animals (fig. 1) and include thousands of lineages, from the mushroom forming fungi, to yeasts, rusts, smuts, molds, and more or less conspicuous critters with interesting morphologies. Fungi complete indispensable ecological roles, most notably decomposition processes, but are also involved in important symbiotic associations and are known to include noteworthy parasites (Alexopoulus, 1996). Fungi have been known and used by humans for centuries, but mycology (the scientific study of fungi) traces ist beginnings to the 18th century, with the development of the microscope (Ainsworth, 1976). While much has been discovered since then, fungi remain today a cryptic and understudied group of organisms. Recent estimates point to 1.5 million fungal species on the planet (Hawksworth, 2001) of which only ~7% have been described (Kirk et al, 2008). Furthermore, fungi assemble in very species-rich communities, making the full documentation of fungal diversity in targeted sites a particularly challenging task. Given the important roles fungi play in the maintenance and functioning of ecosystems, such documentation is often combined with functional perspectives, aimed at understanding the ecology of fungi. Advances in molecular techniques have formed the base for a boost in studies concerning fungal diversity, and the fast development of nextgeneration sequencing technologies promises further progress towards a more thorough understanding of fungal diversity and function. Our current limited knowledge of fungal diversity and biology complicates an assessment of the conservation status of fungal species and has hindered the development of conservation tools and efforts. Furthermore, the absence of expedite and adequate methods to document fungal demographics has made it extremelly difficult to fit fungi into the efforts to currently established IUCN conservation categories. There have been, however,