How do I run multiple instances of Android Studio

Your Android Studio was set to open project in the same window. You can change that, so it asks whether to open new window while opening other project.

Do this:

1. Go to: File -> Settings -> Appearance & Behavior -> System Settings -> Project Opening.
2. Check [x] “Confirm window to open project in”.
3. Now open the other (2nd) project with File -> Open… etc.
4. You will now be asked if you want to open a new window or replace what you already have. Select New Window.

Screenshots:

Older versions:

1. Go to Settings -> General -> Project opening.
2. Check ‘Confirm window to open project in’.
3. Create or open different project
4. You will be asked if open a new window.