On the first line of an interpreter script, the "#!", is the name of a program which should be used to interpret the contents of the file. For instance, if the first line contains "#! /bin/sh", then the contents of the file are executed as a shell script.

You can get away without this, but you shouldn't. All good scripts state the interpretor explicitly. The '!' is also known as intepreter for the script to recognise correct compiler to be used.