Printing email in Gmail is possible, but not obvious, from Android devices. Andy Wolber shows how to do it.

Once Cloud Print is setup, we can open the Gmail app and print, right?
Well, if you're using Chrome on an iPhone, iPad or desktop, then yes. That's exactly how printing works on those devices.
Not Android
To print an email from Gmail on iOS: Tap the triangle in the upper right, then select the device. Simple.
On iOS: print from Gmail to Google Cloud Print
To print an email from Gmail in a desktop/laptop Chrome browser: Click the printer icon to print everything in an email thread. Or, select print from the drop-down menu to print a specific message. Simple.
In laptop/desktop Chrome: print from Gmail to Google Cloud Print
Android
But to print an email from an Android device you need to use the browser, not the app: Open Chrome, login to Gmail, select an email. Print.
On Android: Use Chrome to print an email.
Yes, you read that correctly. You can't print an email from the Gmail app on Android. To print, Android users have to access Gmail in a mobile browser, not the Gmail app.
Gmail on Android lacks a print option
There is one work-around that permits printing without leaving the Gmail app on Android: print-via-email forwarding. First, you enable a secret email address for your printer during a web-setup process. HP printer owners, for example, manage this address online at www.hpeprintcenter.com. Then, you forward an email to your printer's email address from Gmail. The printer will print both the contents of the email and most standard file-format attachments. (To prevent print spam, you can configure the printer to accept print jobs from specified email addresses.) Unfortunately, not all printers support print-via-email forwarding.
Bottom line
So, to recap: you can print from Google's iOS Gmail app. And you can print from Gmail on your laptop or desktop while in Chrome. And you can print from Gmail on Android while in Chrome.
But, as of October 2013, you can't print from Google's Android Gmail app.
Can anyone explain why not?