The cell wall provides physical strength to cells and defines the morphology of fungi. During hyphal development of filamentous fungi, the apical region and the branching sites of the cell are remodeled to support hyphal extension and formation of a new hypha. The cell wall has contact with the environment and thus is the place of first contact with external stresses originating outside of the cells. The cell wall also acts as a matrix for various extracellular proteins such as enzymes and sensor proteins. Budding yeast (Saccharomyces cerevisiae) and filamentous fungi (Aspergillus species) are industrially and medically important fungi belonging to the Ascomycota. These fungi share similar composition in the cell wall although they are morphologically different. Fungal cell walls are usually composed of glucose, mannose, N -acetyl- D -glucosamine, proteins, and lipids. Some glycans composed of galactofuranose or N -acetyl- D -galactosamine are found characteristically in the cell wall of Aspergillus species. In this chapter, we present an overview of current knowledge on cell wall biogenesis and wall-stress sensing in fungi, particularly focusing on recent findings in filamentous fungi.