I decided to start exploring android development and I have some basic questions before I start writing my app. I have an app in my mind. First question concerns compatibility. I want the app to be compatible with all versions of android. I suppose if I use the 1.5 SDK when creating a new project, it will run on 1.6 - 2.1 etc. But if I want to add something that is on a later sdk such as the option for sd save in 2.2? what sdk do i need then for it to be compatible? Secondly, there are a lot of screen resolutions in android devices. Which one do you program on? and if I need it to run ok with all the different resolutions what do I need to do? Thanks in advance.