Microsporidia are unique, obligate intracellular parasites closely related to fungi which have evolved highly specialized mechanisms to adapt, infect, and survive in various hosts ranging from vertebrates to invertebrates. A hallmark of microsporidia is the extrusion of a polar tube in the infection process. These parasites have evolved and undergone extreme genome reduction resulting in loss of many cellular functions, such as mitochondria-based energy production and major biosynthetic pathways. However, they have retained the essential genes for successful host invasion and energy acquisition from the host cells. The compact small-sized genome and reliance on the host demonstrate a distinct evolutionary path, making microsporidia a fascinating subject in evolutionary biology. This chapter provides an overview of microsporidia: covering their biology, life cycle, and genome reduction with a focus on how these features influence their survival and pathogenicity. Furthermore, the chapter explores the emerging biotechnological potentials of microsporidia, particularly in the field of biocontrol of vectors and promising applications in medical science. Although research in the field presents exciting prospects, several challenges remain, including the poorly understood host range, lack of reliable genetic transformational system, difficulties in culturing, and biosafety concerns that must be addressed to fully harness their potential.