Oral candidiasis is a very common localized infection of the mucus membrane of the oral mucosa caused by Candida species. Most commonly, it is caused by the patient's own commensal Candida albicans, but it may also be caused by other Candida species such as C. glabrata, C. tropicalis, and C. krusei. This book reviews briefly on the the dimorphic yeast Candida albicans, its virulence, pathogenicity, host immune factors against candida and pathogenesis of candidal infections in various conditions with numerous lab investigations performed in its diagnosis. A brief note on various candidal strains, fungal morphology, its distribution and classification of various fungal infections has also been reviewed.