**1. Introduction**

Biodegradation is defined as the biologically catalyzed reduction in the complexity of chemical compounds. Indeed, biodegradation is the process by which organic substances are broken down into smaller compounds by living microbial organisms. When biodegradation is complete, the process is called "mineralization". However, in most cases, the term biodegradation is generally used to describe almost any biologically mediated change in a substrate [1]. Fungal diversity is globally estimated to 1.5 million species and consists of an incredibly diverse group of organisms. Organisms studied by mycologists include members of the fungal Kingdom but also others like Protozoa e.g. slime molds [2]. Biodegradation by fungi is also known as mycodegradation. Likewise, bioremediation in which fungi are employed is sometimes called mycoremediation [3]. Fungi are parasitic, saprophytic, mutualistic, and decomposers and grow faster on their substrate and synthesis metabolites to adjust with all the adverse condition and competitor, therefore it has several secondary metabolites, these metabolites serve as a treasure for the new source of potential drugs for human health and the plant health [4]. Fungi have ancient application in human health and nutrition, it produces several enzymes like cellulase, lipase, ligninolytic enzymes, catalase, laccase, etc., alkaloids, pigments, aroma, and flavors, and used in biological control of nematodes, in plants pest control, health benefits by edible fungi [5, 6]. The diversity of fungi play important role in the environment as it acts as decomposers and recycles the organic matter in nature, provides nutrition to plants through mycorrhization [7, 8], and the enzymes secreted by fungi are investigated for the production of the different by-products out of waste

and sludges. Many filamentous fungi are now investigated for the production of biofertilizers [9, 10]. Fungi produce numerous secondary metabolites that are used for human benefit. Despite the benefit of fungi for human health and plant health, it has a negative effect too. The different aspect of fungi effects on human and plant is all due to the potential of the fungi to utilizes the recalcitrants wastes through a process called as biodegradation. In this chapter, the different aspects of fungal biodegradation and its relation to human and plant nutrition have been highlighted.
