The protected internal accessibility means protected OR internal, not protected AND internal. In other words, a protected internal member is accessible from any class in the same assembly, including derived classes. The protected internal access modifier seems to be a confusing but is a union of protected and internal in terms of providing access but not restricting. It allows: • Inherited types, even though they belong to a different assembly, have access to the protected internal members. • Types that reside in the same assembly, even if they are not derived from the type, also have access to the protected internal members. for similar kind of C# questions you can refer this link c# interview questions