This chapter covers a brief discussion on fungal infections. Systemic or invasive candidiasis includes candidemia, disseminated candidiasis, and focal organ involvement. The risk factors include medications, catheter-related causes, and hospitalization. The gold standard for diagnosing systemic candidiasis is a positive culture from the blood or a normally sterile body fluid or site. Antifungal therapy with an echinocandin agent is the treatment of choice for critically ill patients with candidemia and other forms of invasive candidiasis. Aspergillus species are ubiquitous in the environment. The primary route of acquisition is inhalation of aerosolized spores and the principal site of disease is the lung. Diagnosis of invasive aspergillosis is established by tissue biopsy showing Aspergillus in histopathologic and culture specimens that were obtained from a normally sterile site. Mucormycosis is an acute and rapidly progressive, fatal infection that spreads from sinuses retro-orbitally and to the central nervous system (CNS). Diagnosis is confirmed by tissue biopsy and culture. Blood cultures are rarely positive. Treatment requires a combination of high dose conventional or lipid-based amphotericin B and immediate, aggressive surgical debridement. Cryptococcosis, blastomycosis, histoplasmosis, coccidioidomycosis, and sporotrichosis are other fungal infections which are discussed in this chapter.