Is an android mobile phone app that was released Nov 15, 2012 by NianticLabs@Google. It can be downloaded from the play store here.
On July 2014 it was also released for iOS. You can find it in the apple store
Players must choose a faction to join: Enlightened or Resistance
(a change in faction is possible via this link but you lose the progress done and keep only badges won and stats).

When hacking portals occasionally you will obtain Media (videos, images documents). Some of them contain hidden info others are just story related. The ones found so far can be seen here

Occasionally, Niantic leaves hidden codes in messages and bits of media. These codes can be entered into the scanner or on the Intel page and redeemed for AP, XM, and other items.
More info can be found here

• Google's support page for Ingress
• Ingress Agent Field Guide
• Data over time of the scores here
• Map where users can list their location for collaboration. Google map link
• Easy to use portal calculators can be found here and here
• Attack simulator - If you want to plan an attack before going in this is perfect for it
• Field Calculator
• septicyle lists
• calendar formats for septicycles

As anything player made it may contain errors. use them at your own responsibility and feel free to add your own to the list

• DecodeIngress Three part video series how to play
• Perfecto Ong Bautista guide
• Kate Negin newbie guide
• Guide made by wiki users
• Video guide series made by Fevenis on the very basics of ingress interface and some basic concepts
• Martijn's Password Decoding Guide
• Portal: How do they work

The app used to require users to acquire an activation code, during the closed beta, usually by signing up for the wait-list at the Ingress website or from the Niantic Project website. For the sake of record this section is still presented here) You would receive an email like this after some time (this has been months in some cases)
There were other sources for these codes as well:

• Players could invite other players directly with their e-mail address, and local factions were often happy to provide codes to prospective teammates - for example, looking for local-area G+ communities of the faction that the player would desire.
• Users (and on rare occasions googlers) would give away codes or offer puzzles and trivia at irc.irchighway.net #invites
• The Niantic project Facebook page almost every day had some codes hidden in their images (it was advised to use the facebook page download option as facebook sometimes compresses the images too much)
• Sometimes, in the #veruminveniri IRC channel, there was a bot called Limentinus. Sending it a PM will start a trivia game, and answering the question right would get you an invite. After 10 minutes the invite was launched into the channel so if you was not used yet, it's highly likely someone else would pick it up immediately

Known commands

-The words invite(s) or trivia in the main channel activates the reply “Send me a private message if you want to play trivia and win an invite.”

-Asking “Limentinus, how many left?” (or similar phrases) in the main channel activates the reply I currently have over 20 scanner activation codes available to win.. If less than 20 it gives an exact number.

-Saying “Limentinus, rules?” produces the reply Trivia Rules: One invite per player. If you lose, try again another day.You have up to three questions, and three guesses for each. You can ask for a hint if you need to.

-Saying hint in the PM after he asks the question gives you a free hint for the answer.

• Verum Inveniri also occasionally offers puzzles that contain invites when decoded
• Joe Philley and Brandon Badger occasionally give out invites for original artwork or interesting stories
• The character White rabbit seems to do some invite related challenges from time to time (“rabbit holes,” as it refers to).