https://developer.paypal.com/docs/api/

https://developer.paypal.com/docs/

https://developer.paypal.com/docs/integration/mobile/mobile-sdk-overview/

https://developer.paypal.com/docs/integration/admin/manage-apps/

https://github.com/paypal/PayPal-Android-SDK#add-the-sdk-to-your-project

https://developer.paypal.com/webapps/developer/docs/classic/mobile/gs_MPL/

http://tutorials-android.blogspot.kr/2012/05/paypal-intigration-in-android.html  <<==good

http://www.slideshare.net/rschwentker/paypal-mobilepayments

http://stackoverflow.com/questions/18504286/paypal-integration-to-android-application

http://androidcodeexamples.blogspot.kr/2012/06/how-to-integrate-paypal-in-android.html

http://sunil-android.blogspot.kr/2013/10/paypal-android-sdk-with-multiple-in-app.html  <<==Great

https://devblog.paypal.com/working-with-the-new-android-sdk/   <<==Great

http://www.hasmukhbhadani.com/2012/05/paypal-integration-in-android.html

http://ask2mujahed.wordpress.com/2013/07/08/java-paypal-integration-tutorial-1/

http://kishor273.blogspot.kr/2011/07/paypal-integration-in-android.html

https://www.youtube.com/watch?v=NUXtFb1KwPQ

https://www.youtube.com/watch?v=QTO5a1IeBl8