Plasma immersion ion implantation (PIII) has a number of advantages compared to conventional beam-line ion implantation with respect to the surface modification of industrial components and synthesis of novel structures. Since the establishment of the Plasma Laboratory in 1996, the research group in the City University of Hong Kong has embarked on many research and development programs in semiconductors, metallurgy, biomedical engineering, and instrumentation. In this review, we focus on the work done on surface modification and functional thin film fabrication. The surface properties of many materials, such as Ti-6Al-4V alloy and 9Crl8 steel, can be improved dramatically by using the proper PIII processes, and the process window and results are discussed in this paper. One of the advantages of PIII is its ability to treat samples with sophisticated shape, and a myriad of industrial components such as oil pumps and ball bearings can be processed effectively. In these cases, theoretical simulation not only improves our understanding of the interaction of the plasma parameters but also expedites the identification of the optimal processing conditions to attain for instance, uniform implantation dose and the desired modified layer thickness. We will discuss the use of various modeling techniques in PIII-D. In addition, our group pioneers high-frequency, low-voltage PIII which is a very effective method to increase the thickness of the modified zone by enhancing diffusion and elevating the sample temperature. We will discuss the typical process parameters as well as results obtained from SS304 steels. Finally, we will discuss the processes and results pertaining to the fabrication of functional thin films such as of TiO₂ and diamond- like-carbon (DLC) for biomedical applications, Al₂O₃ for optical applications, as well as CeO₂ for semiconductor applications.