Android Open Source Project
The Android Open Source Project, or AOSP for short, is the freely available base version of the mobile operating system Android. Google publishes the blueprint of the system there, allowing manufacturers and developers to use and modify it free of charge.
Every smartphone needs an operating system: the program that controls the screen, launches apps, and manages the hardware. For most phones that aren’t made by Apple, that’s Android. The Android Open Source Project is the publicly accessible base version of this system. Google provides the complete source code there, meaning the human-readable instructions from which the program is built. Anyone may download this source code, modify it, and build their own system from it. It’s usually just called AOSP.
What AOSP means for the phone market
Without AOSP, every phone manufacturer would have to write its own operating system. That is a job worth thousands of person-years. Instead, Samsung, Xiaomi, Motorola, and many others take the finished foundation and put their own interface on top of it. That’s why Android phones look different from one another but essentially work the same at their core.
For companies, this is also a question of independence. When Huawei was banned from using Google services in 2019, the open part of Android remained available to the company nonetheless. Huawei built its own system on this basis. Amazon's Fire tablets and the software of many TVs also come from AOSP, even though no Google logo appears there.
An important distinction: AOSP is not the same as the Android found on a purchased phone. Play Store, Google Maps, Gmail, and Google Search are separate, non-open programs. Manufacturers must sign a contract with Google in order to include them. This exact distinction was at the center of several antitrust proceedings brought by the EU Commission against Google.
From source code to finished system
AOSP consists of several layers. At the bottom sits the Linux kernel, a core program maintained since the 1990s that communicates directly with the processor, memory, and radio chips. Above that lie libraries and services, for example for graphics or Bluetooth. At the very top are the building blocks that apps work with, along with a few simple standard apps like Phone, Clock, and Camera.
The source code resides in public repositories on the internet, split across several hundred sub-projects. Anyone wanting to turn this into a working system downloads everything and has it compiled. Compiling means: a program translates the readable text into machine instructions. On an ordinary computer this takes hours and requires many gigabytes of space. In the end, there is a file that can be installed on a suitable device.
Google controls the development itself. Outside changes can be submitted, but they are only accepted after review by Google developers. AOSP is thus open in the sense of being viewable and usable, but it is not democratically managed. Major new versions are developed internally first and only become public at launch.
AOSP in products and the news
Anyone who’s never heard of AOSP still uses it every day. Checkout systems in supermarkets, onboard computers in cars, information terminals at train stations, and smart TVs frequently run on it. The reason is simple: the system is proven, free, and can be tailored to weak hardware.
AOSP is also known through alternative phone systems. Projects like LineageOS or GrapheneOS build on it and offer longer security updates or more privacy. Tech-savvy users install them on older devices, extending their lifespan by years.
In business news, it’s mostly about power and rules. When Google removes individual building blocks from the open part and moves them into its closed apps, this is seen as a sign of decreasing openness. A common misconception is that Android is therefore a joint project of many companies. In truth, one company determines the direction, and openness is a strategy, not an end in itself.