Book excerpt: Studying defects and imperfections in unconventional superconductors is paramount for fundamental and applied research. Defects play a multifaceted role, from decreasing quality and performance in some situations to enhancing desired properties in others, and as a useful probe and a tool to study the fundamental aspects of superconductivity. The examples are quantum decoherence in superconducting qubits, pinning and critical current in superconducting magnets, and in determining the symmetry of the order parameter, respectively. Studying defects and imperfections can provide insights into the underlying physics of unconventional superconductivity, shedding light on the mechanisms that govern the emergence of superconductivity in these materials, as well as the factors that limit their critical current densities and their stability at elevated temperatures and magnetic fields. Understanding the complex mechanisms through which defects influence the properties of superconductors is key to advancing the development and optimization of high performance superconducting materials for modern technologies.