Fungal secondary metabolites are a large class of structurally diverse compounds of significant ecological roles and high value in industry, agriculture, and medicine. Their biosynthesis includes polyketides, non-ribosomal peptides, terpenoids, and alkaloids, all produced by complex biochemical pathways encoded by biochemical gene clusters (BGCs). This chapter will review the biochemical and genetic basis for these pathways, with an emphasis on the enzymatic steps and precursor molecules leading to the synthesis of bioactive compounds. The molecular regulation of these pathways emphasizes the role of environmental signals, transcription factors, and epigenetic modifications. The development of omics technologies such as transcriptomics, metabolomics, and genomics has changed our view of route creation and control. This allowed not only the construction but also the discovery of novel pathways. The characterization of unknown pathways, the comprehension of complex regulatory networks, and metabolic flux control remain highly challenging tasks despite enormous progress. Future developments, including artificial intelligence and multi-omics integration, may lead to further development in the research of fungal secondary metabolites. The conclusion of this chapter thus underlines the necessity for an interdisciplinary approach toward the effective utilization of these metabolites when it comes to meeting global challenges related to sustainable agriculture and health. The chapter thus covers in-depth basic research on the biosynthesis of secondary metabolites by fungi and how these processes make powerful impacts on science and business.