.apk File — Android Application Package

APK (Android Package Kit) is the file format used to distribute and install applications on the Android operating system. An APK file is a ZIP archive containing the compiled application code (classes.dex in Dalvik bytecode), resources (layouts, drawables, strings), assets, native libraries (.so files for different CPU architectures), the AndroidManifest.xml (declaring permissions, components, and requirements), and a META-INF directory with digital signatures for verification. APK files are the primary distribution format for the Google Play Store and third-party Android app stores. The Android build process compiles Java/Kotlin source code to DEX (Dalvik Executable) bytecode, packages resources, and signs the APK with the developer's certificate. APK files can be sideloaded on Android devices by enabling installation from unknown sources. Android App Bundles (.aab) are now the recommended upload format for the Play Store, which generates optimized APKs for each device configuration, but APK remains the format actually installed on devices. APK files can be analyzed and decompiled using tools like apktool, jadx, and Android Studio's APK Analyzer for security research and debugging.