Direct3D is part of Microsoft's DirectX API. Direct3D is only available for Microsoft's various Windows operating systems (Windows 95 and above) and is the base for the graphics API on the Xbox and Xbox 360 console systems. Direct3D is used to render three dimensional graphics in applications where performance is important, such as games. Direct3D also allows applications to run fullscreen instead of embedded in a window, though they can still run in a window if programmed for that feature. Direct3D uses hardware acceleration if it is available on the graphics card, allowing for hardware acceleration of the entire 3D rendering pipeline or even only partial acceleration. Direct3D exposes the advanced graphics capabilities of 3D graphics hardware, including z-buffering, anti-aliasing, alpha blending, mipmapping, atmospheric effects, and perspective-correct texture mapping. Integration with other DirectX technologies enables Direct3D to deliver such features as video mapping, hardware 3D rendering in 2D overlay planes, and even sprites, providing the use of 2D and 3D graphics in interactive media titles.

Direct3D is a 3D API. That is, it contains many commands for 3D rendering, however since version 8 Direct3D has superseded the old DirectDraw framework and also taken responsibility for the rendering of 2D graphics. Microsoft strives to continually update Direct3D to support the latest technology available on 3D graphics cards. Direct3D offers full vertex software emulation but no pixel software emulation for features not available in hardware. For example, if software programmed using Direct3D requires pixel shaders and the video card on the user's computer does not support that feature, Direct3D will not emulate it. The API does define a Reference Rasterizer (or REF device), which emulates a generic graphics card, although it's too slow to be used in any application to emulate pixel shaders and is usually ignored.

Direct3D's main competitor is OpenGL. There are numerous features and issues that proponents for either API disagree over, see comparison of Direct3D and OpenGL for a summary.