A removable user identity module, or RUIM card, is an identification chip for cellular phones that are made for Code Division Multiple Access (CDMA) networks. A RUIM card holds a user's stored personal information, such as his or her name and account number, cell phone number, phone book, text messages and other settings. It typically is designed to be interchangeable with a subscriber identify module, or SIM card, which serves the same purpose on Global System for Mobile Communication (GSM) networks.

A RUIM card, sometimes called an R-UIM card, gives a cell phone user the ability to switch phones by simply removing the RUIM card and slipping it into another card-enabled phone. The new phone would then be able to make and receive calls on the user's account without having to go through the carrier for activation. A user could, for example, have several phones and switch between them or borrow a friend's phone to make a call with his or her RUIM card. If the user switched to another carrier and wanted to keep his or her old phone, the new carrier could simply issue the customer a new RUIM card to use in his or her existing phone. For this to work, however, the existing phone must be unlocked and compatible with the frequency band of the new carrier.

The idea of a RUIM card originated in the use of SIM cards in GSM networks. GSM, a network technology that competes with CDMA, is popular in most countries outside of North America, especially European countries, and it has a much larger share of the world market than CDMA. SIM cards and RUIM cards typically are designed to be interchangeable in phones, allowing the consumer maximum flexibility. They usually are required to meet the same standards as well. RUIM cards were developed by the CDMA Development Group and 3rd Generation Partnership Project (3GPP) and were approved by the Telecommunications Industry Association (TIA).