Programming languages have been classified into several programming language generations. Historically, this classification was used to indicate increasing power of programming styles. Later writers have somewhat redefined the meanings as distinctions previously seen as important became less significant to current practice.

A first-generation programming language (1GL) is a machine-level programming language. These are the languages that can be directly executed by a central processing unit (CPU). The instructions in 1GL are expressed in binary, represented as 1s and 0s (or occasionally via octal or hexadecimal to the programmer). This makes the language suitable for execution by the machine but far more difficult for human programmer to learn and interpret. First-generation programming languages are rarely used by programmers in the twenty-first century, but they were universally used to program early computers, before assembly languages were invented and when computer time was too scarce to be spent running an assembler.

Examples: assembly languages

Second-generation programming language (2GL) is a generational way to categorize assembly languages.

Examples: C, C++, Java, Python, PHP, Perl, C#, BASIC, Pascal, Fortran, ALGOL, COBOL

3GLs are much more machine-independent (portable) and more programmer-friendly. This includes features like improved support for aggregate data types and expressing concepts in a way that favors the programmer, not the computer. A third-generation language improves over a second-generation language by having the computer take care of non-essential details. 3GLs are more abstract than previous generations of languages, and thus can be considered higher-level languages than their first- and second-generation counterparts. First introduced in the late 1950s, Fortran, ALGOL, and COBOL are examples of early 3GLs.

Most popular general-purpose languages today, such as C, C++, C#, Java, and BASIC, are also third-generation languages, although each of these languages can be further subdivided into other categories based on other contemporary traits. Most 3GLs support structured programming. Many support object-oriented programming. Traits like these are more often used to describe a language rather than just being a 3GL.

Examples: ABAP, Unix shell, SQL, PL/SQL, Oracle Reports, R, Halide