Cling is an interactive C++ interpreter, built on the top of LLVM and Clang libraries. Its advantages over the standard interpreters are that it has command line prompt and uses just-in-time (JIT) compiler for compilation. One of Cling's main goals is to provide contemporary, high-performance alternative of the current C++ interpreter in the ROOT project - CINT. The backward-compatibility with CINT is major priority during the development.