In addition to the unicellular yeast fungi introduced in Chap.  2 , another important species is filamentous fungi that contain multiple nuclei. Many filamentous fungi can also be used for the production of microbial lipids, and have reached the early stage of commercial production. This chapter focuses on the microbial lipid production technology based on these filamentous fungi. Compared with single-cell yeast, the most intuitive feature of filamentous fungi is that the latter exists in the form of Mycelium, which also gives filamentous fungi some special characteristics different from single-cell yeast. For example, the lipid accumulated by this heterotrophic filamentous fungus is often higher in degree of unsaturated fatty acids than yeast lipids. Therefore, filamentous fungi are often used to produce polyunsaturated fatty acids (PUFAs) with high nutritional value in industry. These important PUFAs mainly include linolenic acid (ALA), eicosapentaenoic acid (EPA), docosahexaenoic acid (DHA), linoleic acid (LA), γ-linolenic acid (GLA), and arachidonic acid (ARA).