Fortran was one of the first widely used high-level programming languages when assembly was one of the only ways to program. There had been high-level programming languages before FORTRAN, but it was the first widely successful one.
FORTRAN II in 1958 added more functionality to the language, such as separate compilation of program modules. Also created in 1958 was FORTRAN III, but it was never publicly released. It included the ability to add assembly code into the middle of FORTRAN code.
FORTRAN IV, released in 1961, was a redo of FORTRAN II. It included various improvements, such as removal of machine-dependent glitches. In order to maintain backward compatibility with older FORTRAN programs, a translator for FORTRAN II to FORTRAN IV was released.
The ASA committee began development of a standard for FORTRAN in 1962. This made the production of FORTRAN systems a viable option for vendors and served to increase FORTRAN's popularity. The new standard was released in 1966, and was subsequently known as FORTRAN 66. It became the first high-level programming standard ever.
The next release of FORTRAN was in 1977 and included block statements for IF , THEN , ELSE. The development of FORTRAN slowed, during which times languages such as C and C++ gained popularity. The next three releases of Fortran are unofficially known as Fortran 90, Fortran 95, and Fortran 2003. (Early versions of FORTRAN were capitalized but versions since Fortran 90 have not been.)