**1. Introduction**

Corrosion can be defined as an attack on materials because of an interaction of materials with the surrounding environment. Based on this definition, all materials can corrode. But in practice, the term corrosion is mainly associated with the degradation of metals [1]. Metals are widely used materials due to having remarkable properties such as high electrical and thermal conductivity, ductility, malleability, and high strength. Apart from gold, platinum, and a few others, most metals are prone to corrosion. This problem can be more important when using metal alloys as the type, speed, and rate of corrosion are different for each element. In fact, more than one type of corrosion can occur in the corrosion of alloys. Corrosion is a common and costly phenomenon that should be prevented to avoid irreparable risks such as damage to structures and human life. There are several factors that influence the rate of corrosion including diffusion, temperature, conductivity, humidity, type of ions, pH value, and electrochemical potential [2]. The corrosion rate of metals can be controlled or reduced by taking various measurements. The most common methods include

cathodic protection, galvanizing, painting, and coatings. Coatings are probably the most convenient method to prevent the corrosion of metals due to the low cost, availability of raw materials, flexibility, and simplicity. There are many different types of industrial coatings, including organic (alkyd coatings, epoxy coating, polyurethane coatings, etc.) and inorganic coatings (ceramic coatings, metalized coating, etc.).

Despite having many advantages, coatings are subject to problems such as cracking and degradation. Therefore, they must be repaired or replaced. Being exposed to a corrosive environment for a long time leads to the weakening of the mechanical properties of the coating, and as a result, microcracks form and propagate. The failure of the coatings is inevitable and hence they must be repaired or replaced. In order to improve the properties of the coatings, several methods such as adding fillers in a polymer matrix have been proposed and implemented. Various fillers including zinc oxide, titanium dioxide, and silicon dioxide have been used and commercialized which enhance both mechanical properties and corrosion inhibition performance of coatings. During the past two decades, new-generation protective coatings, self-healing coatings, have been introduced and developed that can repair the damage caused by corrosive media and as a result, increase the coating lifetime. Self-healing coating has become a research hotspot in the coating field. Thus underlying their properties, mechanism, and synthesis procedures could be interesting. However, the development of these coatings is still in its early stages and it is very important to know their various aspects, including their properties, mechanism, performance, and application. This chapter provides basic information about metal corrosion and the development of methods to inhibit this phenomenon. In addition, different mechanisms of self-healing materials and published reports in this field are reviewed.
