Surface modification processes can be categorized into two main parts: wet processes and dry processes. Wet surface modification techniques involve chemical and/or physical modification of a material's surface through the usage of various chemical agents that are either in liquid state during the processes or dissolved in a suitable solvent before their applications on the material's surface. Vapor deposition methods do not involve any wet material on a substrate surface. Furthermore, a vapor deposition process usually occurs under vacuum or purged conditions at which only precursor or carrier molecules exist. Therefore, vapor deposited coatings are quite pure. The impurities introduced into the coatings by the solvent may lead to impure films that may not be suitable for many end uses. This chapter discusses various kinds of vapor deposition processes used to deposit functional coatings onto various substrates and introduces some industrially important wet processes.