Scalability is a performace matrix , it is the ability of a software program to continue to function smoothly as additional volume, or work is required of it. Also, o ne can say it is the ability to expand the number of users or increase the capabilities of a computing solution users without making major changes to the systems or application software. To me, it is wrong to blankly say that Stateful beans are not scalable. I think it should say "less scalable" rather than "not scalable" . Yes they have more overhead than the stateless beans, but sateful beans are there for a purpose , to maintain state between method invocations. It would be a overkill if one uses stateful bean for a business rule when the same thing can be done with a stateless bean. Reg. examples, it is hard to give you a example for scalability as one can experience when the system is under load testing or under peak load. if you would really like a example , then you could download one of the free load testing tools and run them against your application.