Common Intermediate Language (CIL) is the core of the language. NET. Though. NET developers often use high-level language (like C # or VB. NET) to develop their system, they can use CIL to do anything permitted by.NET-specification that is not the case for C # and VB. NET. This knowledge is essential to creating dynamic types, a strong part of the NET Framework .. In CIL Programming: Hood of. In NET, Jason Bock offers in-depth tutorial on programming in CIL. Bock also covers the ways in which C #, VB. NET, and non-Microsoft languages emit CIL, and how they differ.