This lecture covers the nuts and bolts of IDL programming. There won't be much graphics but we will look at many things which will help you to make good use of IDL. This is the bit of the course where I assume that you can program in C or Fortran. I will, for example, explain what sorts of variables there are in IDL, but I won't explain what a variable is in any detail. If you don't like the way I present the material, the place to look it up is the section of the on-line manual called ``Building IDL Applications''.