BlackBerry OS is the proprietary software platform made by Research In Motion for its BlackBerry line of handhelds. BlackBerry OS provides multi-tasking, and makes heavy use of the device's specialized input devices, particularly the trackball or touchscreen. The OS provides support for MIDP 1.0 and WAP 1.2. Previous versions allowed wireless synchronization with Microsoft Exchange Server's e-mail and calendar, as well as with Lotus Domino's e-mail. The current OS 4 provides a subset of MIDP 2.0, and allows complete wireless activation and synchronization with Exchange's e-mail, calendar, tasks, notes and contacts, and adds support for Novell GroupWise and Lotus Notes when used in conjunction with BlackBerry Enterprise Server.

Updates to the BlackBerry OS may be available if made available by carrier via the BlackBerry OTASL (over the air software loading) service.

Third-party developers can write software using these APIs, and proprietary BlackBerry APIs as well, but any application that makes use of certain restricted functionality must be digitally signed so that it can be associated to a developer account at RIM. This signing procedure guarantees the authorship of an application, but does not guarantee the quality or security of the code.