Ferrofluids are a class of smart materials that exhibit both exceptional magnetic properties and dynamic fluidic behavior. These unique materials are composed of nanoscale magnetic particles suspended within a carrier liquid, which allows them to maintain their fluidic nature while simultaneously responding to the influence of external magnetic fields. Their distinctive combination of magnetism and fluidity has enabled significant advancements in various areas, such as precision engineering, biomedical technologies, thermal management systems, soft robotics, and microfluidics. This chapter provides an overview of ferrofluids, presenting their fabrication methods, fundamental working mechanisms, and applications from different fields.