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During a design session a few folks in my team had questions on using a static class vs a class with static methods. We hit upon this when designing utility classes and extension methods.During the course of this discussion some of us were surprised about what I felt was basic knowledge and I was also caught out on a few which led me to documenting this down below. Static Class Marking a class as static means that a compile time check will be conducted to ensure that all members of the class are static. Since the CLR does not have a notion of static, marking a class as static translates it to an abstract sealed class. ( conversly you cannot mark a static class as abstract) Static classes always inhert from Object and you cannot have it derive from another class. You cannot inherit from a static class. Static classes cannot implement an interface. You cannot obviously instantiate a static class. It cannot have constructors and the compiler also does not create a default parameterless constructor. Defining extensions in C# requires us to implement the static extension methods in a static class. There is a minor performance gain to using static methods as documented in this code analysis performance tip. The performance gain is due to the fact that instance methods always use the this instance pointer as the first parameter which is a small overhead. Instance methods also implement the callvirt instruction in IL which also leads to a very small overhead. Non Static Class A non-static class can have static members. ( both methods and fields ). You can create an instance of a Non static class with static methods. Factory pattern is an example of a Non Static class implementing a static method to control object instatiation. Microsoft docs has an article on this topic here . ...