IBM System z10 is a line of IBM mainframes. The z10 Enterprise Class (EC) was announced on February 26, 2008. On October 21, 2008, IBM announced the z10 Business Class (BC), a scaled-down version of the z10 EC. The System z10 represents the first model family powered by the z10 quad core processing engine. Its successors are the zEnterprise System models introduced in 2010 and 2012.

The number of "characterizable" (or configurable) processing units (PUs) is indicated in the hardware model designation (e.g., the E26 has 26 characterizable PUs). Depending on the capacity model, a PU can be characterized as a Central Processor (CP), Integrated Facility for Linux (IFL) processor, z Application Assist Processor (zAAP), z10 Integrated Information Processor (zIIP), or Internal Coupling Facility (ICF) processor. (The specialty processors are all identical and IBM locks out certain functions based on what the processor is characterized as.) It is also possible to configure additional System Assist Processors, but most customers find the mandatory minimum SAP allocation sufficient.

There are more physical PUs in a machine than characterizable PUs. For example, the E12 has 17 PUs, of which only 12 are characterizable. The remainder is a mixture of spares and mandatory minimum SAPs. The SAPs provide I/O assistance, system accounting, and other critical system functions.

The System z10 supports the following IBM operating systems: z/OS, z/VSE, z/VM, and z/TPF (and its immediate predecessor, TPF/ESA). Other operating systems available include Linux on System z, OpenSolaris for System z, UTS, and MUSIC/SP (at least in principle). A product in development by Mantissa Corporation, z/VOS, was announced in 2008 to run other operating systems developed for x86 architectures (such as Windows and x86 versions of Linux), later renamed to z86VM and the Linux support is in beta, and "has no plans to support 64 bit", but as of 2019, it has a bug for Windows so not even a beta version for it is available.

In addition to much higher performance, System z10 introduced a number of new mainframe features. Some of the more notable enhancements include:

The System z10 adds hardware-based 192-bit and 256-bit Advanced Encryption Standard (AES) in addition to the 128-bit AES support already available on the z9.

The System z9 was the first commercial server to add IEEE 754 decimal floating point instructions, although these instructions were implemented in microcode with some hardware assists. The System z10 implements the main IEEE 754 decimal floating point operations in a built-in, integral component of each processor core and instruction set architecture. As examples, Enterprise PL/I, XL C, and the z/OS Java BigDecimal class can exploit hardware decimal floating point.

The System z10 processor adds numerous new instructions, primarily concentrated on improving the efficiency and performance of compiled code. The z/OS Java SDK exploits these additional instructions when running on a z10. On July 7, 2009, IBM disclosed z/VM Version 6.1, a new version which requires the additional instructions only available in the System z10 and future models.