The main concern of this chapter is to present invasive fungal infections in critically ill patients. Fungal infections are rising globally. Many diverse clinical conditions have been found to be significantly associated with risk of invasive fungal infections (IFI). Based on these risk factors risk prediction models have been designed. Fungal infections are difficult to diagnose in early phase due to absence of any specific clinical feature and poor sensitivity of the culture-based methods. Prediction on microbiological parameters only, prediction on the basis of clinical parameters, and prediction on the basis of both microbiological and clinical parameters are the risk prediction models of IFI. Candida albicans, candida glabrata, candida parapsilosis, candida tropicalis, candida krusei and aspergillosis are canidida infections. Prophylaxis, empirical therapy, pre-emptive therapy and targeted therapy are the treatment strategies for canidida infections. Polyenes-Prototype Amphotericin B, Triazole and Echinocandins are basic pharmacology of antifungals.