This thesis describes how the use of more than one type of programminglanguages can be useful in high-performance computing. Scriptinglanguages like Python and Perl are used for control and computationalsteering, while compiled languages as C and Fortran are used for thenumerically intensive tasks. How to efficiently call compiled codefrom scripting languages is discussed in detail, and numerousexamples show how this can be done. The examples show that acombination of e.g. Python and Fortran is an option very much worthconsidering for numerical applications. The combination can result inapplications with both run-time efficiency and flexible computationalsteering options. There are even good chances that development timefor such applications compare very favorably with more traditionalnumerical applications.