NeXTSTEP（又写作NeXTstep、NeXTStep、NEXTSTEP)是由NeXT.Inc所开发的操作系统。NeXT是已故苹果电脑CEO乔布斯在1985年离开苹果电脑后所创立的公司。

这套系统是以Mach和BSD为基础，以Objective-C作为原生语言，具有很先进的GUI。1.0版推出时间是在****年9月18日。刚开始NEXTSTEP只能在NeXT电脑的Motorola 68000上运行，1992年推出PC版的NEXTSTEP 486。3.1版和3.2版分别在1993年的5月及10月推出，但是终究失败。最后版本3.3在1995年发布，平台也已经不限于Motorola 68000家族，亦可在IBM PC x86、Sun SPARC及HP PA-RISC等平台上运行。后来苹果电脑在1997年2月将NeXT买下，成为Mac OS X的基础。

NeXTSTEP is a discontinued object-oriented, multitasking operating system based on UNIX. It was developed by NeXT Computer in the late 1980s and early 1990s and was initially used for its range of proprietary workstation computers such as the NeXTcube and later ported to several other computer architectures. Although relatively unsuccessful at the time, it attracted interest from computer scientists and researchers. It was used as the original platform for the development of the Electronic AppWrapper, the first commercial electronic software distribution catalog to collectively manage encryption and provide digital rights for apps and digital media, a forerunner of the modern 'App Store' concept. It was also the platform on which Tim Berners-Lee created the first web browser. After the purchase of NeXT by Apple, it became the source of the popular operating systems OS X, iOS, and now watchOS and tvOS. Many bundled OS X apps, such as TextEdit, Mail and Chess, are descendants of NeXTSTEP applications.