**1. Introduction**

Characterization is a vital tool in elucidating the characteristics of material systems and ascertaining their suitability for various applications. Characterization is also an indispensable technique for quantifying self-repairing capabilities of various material classes. A self-healing material is a material designed to mimic nature, self-repair and restore its partial or original characteristics, thereby prolonging its service life like a biological system after encountering some form of damage induced by its service environment [1, 2].

Developing a man-made material capable of sensing and self-repairing in response to changes in the operating environment is a challenging task. This is because it takes a great exploit to design and process a synthetic material to mimic very closely the nature-designed mechanism of self-repair obtained in complex biological architectures. Numerous design approaches and preparatory routes have been attempted by research community to create self-healing abilities in different material classes for many applications. The material classes exploited so far include polymers, metals, ceramics, cements, coatings and composites [3].

Another huge task is quantifying the material's capability to self-repair and its suitability for a specific application via characterization techniques. Several techniques have been employed to evaluate and quantify self-healing capacities and effectiveness in each of above material classes. Nevertheless, challenges arise in the characterization of self-healing materials as evaluation methods are not only materials and application specific, but also depend on the mechanism of the self-healing process. More so, self-healing processes take place on a very small length scale requiring sophisticated experimental procedures and equipment to unravel the mechanism of self-healing. Furthermore, it is important to establish a uniform testing procedure and standard for different material groups for better understanding of the concept [4]. This chapter surveys the main techniques applied to reveal the damage-restoring mechanisms in some material classes, but begins with a brief survey of preparatory routes and mechanisms of self-repair in the different materials classes.
