What is the difference between compileSdkVersion and targetSdkVersion?

I have looked at the documentation for building with Gradle, but I'm still not sure what the difference between compileSdkVersion and targetSdkVersion is.

All it says is:

The compileSdkVersion property specifies the compilation target.

Well, what is the "compilation target"?

I see two possible ways to interpret this:

1. compileSdkVersion is the version of the compiler used in building the app, while targetSdkVersion is the "API level that the application targets". (If this were the case, I'd assume compileSdkVersion must be greater than or equal to the targetSdkVersion?
2. They mean the same thing. "compilation target" == "the API level that the application targets"
3. Something else?

I see that this question has been asked before, but the one answer just quotes the doc, which is what is unclear to me.

Solution 1:

compileSdkVersion

The compileSdkVersion is the version of the API the app is compiled against. This means you can use Android API features included in that version of the API (as well as all previous versions, obviously). If you try and use API 16 features but set compileSdkVersion to 15, you will get a compilation error. If you set compileSdkVersion to 16 you can still run the app on a API 15 device as long as your app's execution paths do not attempt to invoke any APIs specific to API 16.

targetSdkVersion

The targetSdkVersion has nothing to do with how your app is compiled or what APIs you can utilize. The targetSdkVersion is supposed to indicate that you have tested your app on (presumably up to and including) the version you specify. This is more like a certification or sign off you are giving the Android OS as a hint to how it should handle your app in terms of OS features.

For example, as the documentation states:

For example, setting this value to "11" or higher allows the system to apply a new default theme (Holo) to your app when running on Android 3.0 or higher...

The Android OS, at runtime, may change how your app is stylized or otherwise executed in the context of the OS based on this value. There are a few other known examples that are influenced by this value and that list is likely to only increase over time.

For all practical purposes, most apps are going to want to set targetSdkVersion to the latest released version of the API. This will ensure your app looks as good as possible on the most recent Android devices. If you do not specify the targetSdkVersion, it defaults to the minSdkVersion.

Solution 2:

As a oneliner guide:

minSdkVersion <= targetSdkVersion <= compileSdkVersion

Ideally:

minSdkVersion (lowest possible) <= targetSdkVersion == compileSdkVersion (latest SDK)

Read more from this great post by Ian Lake