Project Ara was a modular smartphone project under development by Google. The project was originally headed by the Advanced Technology and Projects team within Motorola Mobility while it was a Google subsidiary. Google retained the ATAP group when selling Motorola Mobility to Lenovo, and it was placed under the stewardship of the Android development staff; Ara was later split off as an independent operation. Google stated that Project Ara was being designed to be utilized by "6 billion people": 1 billion current smartphone users, and 5 billion feature phone users.

Under its original design, as envisioned by NewDealDesign, under the leadership of Gadi Amit, Project Ara was intended to consist of hardware modules providing common smartphone parts, such as processors, displays, batteries, and cameras, as well as modules providing more specialized components, and "frames" that these modules were to be attached to. This design would allow a device to be upgraded over time with new capabilities and upgraded without requiring the purchase of an entire new device, providing a longer lifecycle for the device and potentially reducing electronic waste. However, by 2016, the concept had been revised, resulting in a base phone with non-upgradable core components, and modules providing supplemental features.

Google planned to launch a new developer version of Ara in the fourth quarter of 2016, with a target bill of materials cost of $50 for a basic phone, leading into a planned consumer launch in 2017. However, on September 2, 2016, Reuters reported that two non-disclosed sources leaked that Alphabet's manufacture of frames had been canceled, with possible future licensing to third parties. Later that day, Google confirmed that Project Ara had been shelved.

Google intended Project Ara to lower the entry barrier for phone hardware manufacturers so there could be "hundreds of thousands of developers" instead of the existing oligarchy of phone manufacturers.

The Project Ara concept consisted of modules inserted into metal endoskeletal frames known as "endos." The frame would be the only component manufactured by Google. The frame was the switch to the on-device network linking all the modules together. Google planned two sizes of frames on launch; a "mini" frame about the size of a Nokia 3310 and a "medium" frame about the size of a Nexus 5. Google also planned a "large", phablet frame about the size of a Samsung Galaxy Note 3 to be released in the future. Frames have slots on the front for the display and other modules. On the back are additional slots for modules. Each frame was expected to cost around US$15. The data from the modules can be transferred at up to 10 Gbit/s per connection. The 2×2 modules have two connections and would allow up to 20 Gbit/s.

Modules would provide common smartphone features, such as cameras and speakers, but could also provide more specialized features, such as medical devices, receipt printers, laser pointers, pico projectors, night vision sensors, or game controller buttons. Each slot on the frame accepted any module of the correct size. The front slots are of various heights and took up the whole width of the frame. The rear slots had standard sizes of 1×1, 1×2 and 2×2. Modules were to be hot-swapped without turning the phone off. The frame also included a small backup battery so the main battery can be hot-swapped. Modules were originally to be secured with electropermanent magnets, but this was replaced by a different method. The enclosures of the modules were planned to be 3D-printed, but due to the lack of development in the technology, Google opted instead for a customizable molded case.

Google intended to sell a starter kit where the bill of materials is US$50 and includes a frame, display, battery, low-end CPU and WiFi. Google planned to provide an open development process for modules, and would not have required manufacturers to pay a license fee. Modules were to be available both at an official Google store and at third-party retailers. Similarly to Android apps, an Ara device would be configured by default to only accept modules officially certified by Google, but users would have been able to disable this.

Project Ara was developed and was led by Paul Eremenko, who in 2015 became CEO of the Airbus Group Silicon Valley technology and business innovation center. The project fell under Regina Dugan, who runs Google's Advanced Technology and Projects (ATAP) organization. Both Eremenko and Dugan worked previously at DARPA, where Eremenko originated the fractionated spacecraft concept and ran the Adaptive Vehicle Make program before heading the Tactical Technology office . The core Project Ara team at Google consisted of three people, with most of the work being done by outside contractors, such as NK Labs, a Massachusetts-based engineering firm. NK Labs then subcontracted the firm Leaflabs to do firmware development, and they later became the primary firmware developers in a direct contract with Google. The main physical concept design of the Frame and Modules was created by NewDealDesign a San Francisco based Technology design studio that was commissioned by ATAP to lead the design of the project. That was selected from 11 different configurations analyzed by the joint team. The company 3D Systems was contracted to experiment with 3D printing of electrical components, which could further the goal of mass customization.