While small test programs existed since the development of programmable computers, the tradition of using the phrase "Hello world!" as a test message was influenced by an example program in the book The C Programming Language. The example program from that book prints "hello, world" (without capital letters or exclamation sign), and was inherited from a 1974 Bell Laboratories internal memorandum by Brian Kernighan, Programming in C: A Tutorial, which contains the first known version: #include main() { printf("hello, world "); } Source: Wikipedia