The exploration of the wettability mechanisms in coating materials aims to elucidate the critical factors and underlying principles that govern this important property. By examining how wettability influences the performance and application of coatings, we can better understand the strategies to optimise and innovate in this dynamic field. Understanding the mechanism of wettability is crucial for the design, application, and performance of coating materials. It directly affects adhesion, durability, corrosion resistance, aesthetic qualities, ease of application, and environmental impact. This chapter looks into the wettability mechanism, surface wetting characteristics, adhesion effect, surface energy, surface roughness, chemical compatibility, surface modification, wettability in different applications, and the relevance of wettability. By controlling wettability, manufacturers can enhance the functionality and longevity of coatings, ensuring they meet the specific demands of various applications. Extremely wetting materials, like superhydrophilic and superhydrophobic surfaces, have garnered a lot of interest due to their potential applications in a variety of fields, including drag-reduction systems, anti-corrosive coatings, anti-fog windows, self-cleaning textiles, and effective water transportation.