Using multiple class libraries allows us to re-use code in other applications as well as keep code safe by limitin other projects knowledge of it. These multiple projects keep the code contained but also extensible for other uses. The article below contains some syntax and concepts we haven't seen before; what is important about this article is step 7. The programmer creates their own class library (dll) and then uses it as a reference in another project so they don't have to rewrite the same code over again.