The unidirectional (UD) fiber-reinforced layers frequently used in modern fiber composite laminates are special representatives of UD materials that typically consist of an isotropic matrix and a unidirectional fiber reinforcement. Due to the microstructurally inhomogeneous structure of these UD materials and the given anisotropy with regard to both the elastic properties and the strength properties, the strength analysis of a laminate with fiber-reinforced layers generally proves to be significantly more complex than with homogeneous isotropic materials. One of the reasons for this is that there are different types of failure, such as fiber fracture, matrix fracture, fiber-matrix delamination and delamination of the layers from each other. As a consequence of this, it is not necessarily the stress components with the highest magnitudes that are particularly critical to failure within a laminate; it can also be comparatively small stress components if these are associated with a relatively small anisotropic strength. This chapter provides an overview of common failure criteria for composite laminates made of layers of fiber-reinforced plastics.