Thefirsthelloworld

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 " " (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:
 * 1) include 

main { printf("hello, world\n"); }

The first known instance of the usage of the words "hello" and "world" together in computer literature occurred earlier, in Kernighan's 1972 Tutorial Introduction to the Language B, with the following code: main { extrn a, b, c;  putchar(a); putchar(b); putchar(c); putchar('!*n'); } a 'hell'; b 'o, w'; c 'orld';

Source: [Wikipedia]