In the mid-1990s, a new class of optical fibers emerged: the microstructured optical fiber (MOF) [1,2]. In these fibers, light is guided by a complex microstructure that often, but not always, includes air holes running along the fiber length. Due to their enormous scientific and technological potential, these fibers have been a major field of study in academic and industrial photonic research during the past two decades. This chapter provides a brief overview of the major types and applications of MOFs, along with a short discussion on their modeling and fabrication.