'''Source-code compatibility''' (source-compatible) means that a program can run on [[central processing unit|computer]]s (or operating systems), independently of [[binary-code compatibility]] and that the [[source code]] is needed for [[Software portability|portability]].
The source code must be [[compiler|compiled]] before running, unless the computer used has an [[Interpreter (computing)|interpreter]] for the language at hand. The term is also used for [[assembly language]] compatibility, where the source is a [[human-readable]] form of [[machine code]] that must be converted into numerical (i.e. executable) machine code by an [[Assembly language#Assembler|assembler]]. This is different from [[binary-code compatibility]], where no recompilation (or assembly) is needed.
Source- compatibility is a major issue in the developing of computer programs. For example, most [[Unix]] systems are source-compatible, as long as one uses only standard [[library|libraries]]. [[Microsoft Windows]] systems are source-compatible across one major family (the [[Windows NT]] family, from [[Windows NT 3.1|NT 3.1]] through [[Windows 8.1]], or the family that includes [[Windows 95]], [[Windows 98]], and [[Windows Me]]), with partial source compatibility between the two families.
