OnStar Corporation is a wholly-owned subsidiary of General Motors which provides subscription-based communications, monitoring and tracking services throughout the United States and Canada. OnStar services are only available currently on vehicles manufactured by General Motors, however service was available for a short time on vehicles produced by Acura, Audi, Subaru and Volkswagen through a licensing agreement. The service is available for all vehicles that have the factory-installed OnStar hardware.

It consists of both communication, through AMPS (primary) or CDMA (secondary) mobile phone networks (usually Verizon Wireless and/or Sprint Nextel and/or AT&T Mobility (via AMPS) in the United States and Telus and/or Bell Mobility and/or Rogers Wireless (via AMPS) in Canada), and location information using GPS technology. Drivers and passengers can use its audio interface to contact OnStar representatives for emergency services, vehicle diagnostics and directions. OnStar equipped vehicles with an active subscription will also contact representatives, based out of Troy, Michigan; Charlotte, North Carolina; Tondo, Manila; Makati, Philippines; and Oshawa, Ontario in the event of a collision where the airbags are deployed. Newer models will contact OnStar in any type of collision whether airbags deploy or not. This new service is called Advanced Automatic Collision Notification (AACN) and is designed to greatly enhance emergency response efforts.

When a driver presses the Red OnStar Emergency button or Blue OnStar button, current vehicle data and the user's GPS location are immediately gathered. This information is then sent to OnStar. OnStar Emergency calls are routed to the OnStar Center with highest priority. Two centers exist to receive emergency calls: Charlotte, North Carolina and Oshawa, Ontario; and all centers are open 24 hours a day.

Starting 2009, General Motors will equip new vehicles with an updated version that allows police to remotely halt the vehicle. Customers can opt out of that function, but critics doubt that this decision will be honored in all cases. Also it could give someone who hacked into the system control over the car.

Verizon Wireless currently offers the "America's Choice Plan with OnStar," which is a bundle plan between Verizon Wireless service and OnStar service. With this plan, the Verizon Wireless phone is the "primary line" and the OnStar device is the "secondary line." This plan is actually based around the "Family SharePlan," with rates starting at $69.99 USD for 700 minutes.