Thin films have diverse applications in energy storage, electronic devices, biomedical implants, and optical coatings. Researchers are exploring novel materials, deposition techniques, and functionalisation strategies to unlock new opportunities. The chapter discusses substrate synthesis and surface modification, focussing on vinyl polymers, polyacrylamides, polyphthalamides, polystyrene, polyimides, polyketones, zwitterionic compounds, and celluloses. It also discusses the role of inorganic materials in thin film applications. Surface modification and functionalisation of inorganic thin films involve grafting from and grafting to approaches, providing precise control over surface chemistry and composition. Techniques like surface-initiated polymerisation, atom transfer radical polymerisation, and iCVD allow controlled chain growth and versatile surface functionalities. Superhydrophobic and superhydrophilic thin films are used in various fields, including multilayered packaging, membrane separation, sensing technologies, membrane separation, catalytic systems, and pharmaceutical delivery.