Code in interpreted languages is is handled by an interpreter. The interpreter alternates between translating the source code from a higher level language to machine code and executing the machine code. Interpreters tend to be easier to right, but also operate less efficiently than Compilers Compilers treat translation of source code to machine code and execution of the machine code to be two different batch jobs; they perform the first, then the second. This is good because it tends to lend itself towards type safety and other static semantic checks much more easily, which in turn goes a long way towards dynamic semantic checks and more efficient code execution. However, compilers tend to be a lot more difficult to write and still more difficult to optimize than interpreters.