| X++ | — | — | — | — |
| X10 | 2004 | concurrent computing, array programming, object-oriented programming | static typing, safe typing, strong typing | — |
| XACML | — | semi-structured data, declarative programming | — | — |
| XBasic | — | — | — | — |
| XBLite | — | procedural programming | dynamic typing | — |
| XC | 2005 | concurrent computing | — | — |
| XL | 2000 | functional programming, imperative programming, multi-paradigm programming | strong typing | — |
| XLNT | 1997 | — | — | — |
| XML | 1998 | — | — | 1 |
| XML User Interface Language | 1999 | — | — | — |
| XOD | 2016 | dataflow programming, declarative programming, functional reactive programming, visual programming language | — | — |
| Xojo | 1996 | object-oriented programming | — | — |
| XOTcl | 2000 | event-driven programming, functional programming, imperative programming, multi-paradigm programming, object-oriented programming | dynamic typing | — |
| XPath | 1999 | — | — | 1 |
| XPL | 1967 | procedural programming, structured programming | — | 3 |
| XPL0 | 1976 | procedural programming | — | — |
| XProc | — | declarative programming | — | — |
| XProfan | 1990 | — | — | — |
| XQuery | 2007 | functional programming, declarative programming, modular programming | dynamic typing, static typing, strong typing | — |
| XSB | — | logic programming | — | — |
| XSLT | 1999 | declarative programming | — | — |
| Xtend | 2011 | functional programming, imperative programming, object-oriented programming | static typing, inference typing, strong typing | — |