The Nintendo Switch system software (also known by its codename Horizon) is an updatable firmware and operating system used by the Nintendo Switch and Nintendo Switch 2 hybrid video game consoles. It is based on a proprietary microkernel. The user interface (UI) includes the game library organized in a horizontal row, with numerous additional options and shortcuts underneath.

Nintendo has released only limited information about the Switch's internals to the public. However, computer security researchers, homebrew software developers, and the authors of emulators have all analyzed the operating system in great depth.

Notable findings include that the Switch operating system is codenamed Horizon, that it is an evolution of the Nintendo 3DS system software, and that it implements a proprietary microkernel architecture. All drivers run in userspace, including the Nvidia driver which the security researchers described as "kind of similar to the Linux driver". The graphics driver features an undocumented thin API layer, called NVN, which is "kind of like Vulkan" but exposes most hardware features like OpenGL compatibility profile with Nvidia extensions. All userspace processes are sandboxed and use Address Space Layout Randomization (ASLR), a computer security technique involved in preventing exploitation of memory corruption vulnerabilities.

Nintendo made efforts to design the system software to be as minimalist as possible, with the home menu's graphical assets using less than 200 kilobytes. This minimalism is meant to improve system performance and launch games faster.

As early as July 2018, Nintendo has been trying to counter Switch homebrewing and piracy. Measures include an online ban, and on the hardware side, patching of the Tegra SoC to prevent exploits. On 11 December 2018, Nintendo sued Mikel Euskaldunak for selling a Switch modification that can play pirated games. Since August 2019, the difficulty of homebrewing has gone up, as the new Mariko chip replaced the old Erista chip. After the release of the Lite in late 2019, tools for hacking all Switch consoles were announced. In September 2020, Gary Bowser was arrested in the Dominican Republic, and later appeared in court in the USA afterwards. The prosecution alleges that Bowser was a piracy group leader.

Despite popular misconceptions to the contrary, Horizon is not largely derived from FreeBSD code, nor from Android, although the software license and reverse engineering efforts have revealed that Nintendo does use some code from both in some system services and drivers. For example, the networking stack in the Switch OS is derived at least in part from FreeBSD code. Nintendo's use of FreeBSD networking code is legal as it is made available under the permissive BSD license, and not even particularly unusual – for instance and interface, the Microsoft Windows TCP/IP stack (used since at least 2000 and XP) was originally derived from BSD code in a similar fashion, using part of its TCP/IP code for its implementation of TCP/IP, which was legal.^{[better source needed]}

Components derived from Android code include the Stagefright multimedia framework, as well as components of the graphics stack including the display server (derived from SurfaceFlinger) and the graphics driver (which seems to be derived from Nvidia's proprietary Linux driver).

Although a full web browser intended for general browsing is not available on the console as of January 2025^[update], several so-called 'applets' are included which utilise the WebKit rendering engine to display web content within a stripped back interface. A WebKit-powered applet is used to allow users to log in to captive portals when connecting to certain wireless networks, as well as for operating system features such as the Nintendo eShop, social media integrations, and digital manuals.