Nanotechnology has significantly transformed the field of materials science, enabling the design of functional oxides with tailored structural and electronic properties. Among them, zirconia (ZrO2) stands out due to its polymorphism, high ionic conductivity, low thermal conductivity, chemical stability, and radiation resistance, making it suitable for applications in energy, microelectronics, and nuclear systems. The properties of zirconia are strongly phase-dependent, with the tetragonal and cubic polymorphs offering superior performance over the monoclinic phase. Achieving and stabilizing these phases at room temperature have therefore been central research objectives. Energetic ion beams provide a versatile tool for the synthesis, modification, and engineering of zirconia, offering precise control over defect creation, oxygen vacancy concentration, grain size, and phase stability. By tuning ion parameters such as energy, fluence, and ion species, structural and microstructural transformations can be achieved that are difficult to realize through conventional thermal methods. This chapter reviews the fundamentals of ion–solid interactions, outlines synthesis and characterization approaches, and emphasizes the role of ion beams in enhancing zirconia’s properties. Applications in oxygen sensors, solid oxide fuel cells, thermal barrier coatings, optical devices, and nuclear reactor materials are highlighted. Finally, the chapter discusses current challenges, including scalability and long-term stability, and identifies future directions where ion-beam engineering can drive advances in next-generation functional materials.