PDL (``Perl Data Language'') gives standard perl the ability to COMPACTLY store and SPEEDILY manipulate the large N-dimensional data arrays which are the bread and butter of scientific computing. The idea is to turn perl in to a free, array-oriented, numerical language in the same sense as commerical packages like IDL and MatLab. One can write simple perl expressions to manipulate entire numerical arrays all at once. For example, using PDL the perl variable $a can hold a 1024x1024 floating point image, it only takes 4Mb of memory to store it and expressions like $a=sqrt($a)+2 would manipulate the whole image in a few seconds. A simple interactive shell (perldl) is provided for command line use together with a module (PDL) for use in perl scripts.