|Initial release||May 15, 2013|
Google Hangouts is a communication platform developed by Google which includes instant messaging, video chat, SMS and VOIP features. It replaces three messaging products that Google had implemented concurrently within its services, including Google Talk, Google+ Messenger (formerly: Huddle), and Hangouts, a video chat system present within Google+. Google has also stated that Hangouts is designed to be "the future" of its telephony product, Google Voice, and integrated some of the capabilities of Google Voice into Hangouts. You can use people's Google+ accounts to message them. 
Prior to the launch of Hangouts, Google had maintained several similar, but technologically separate messaging services and platforms across its suite of products. These have included the enterprise-oriented Google Talk (based on XMPP), Google+ Messenger, and the Hangouts feature of Google+, which provided chat, voice, videoconferencing features. However, its increasingly fragmented and non-unified suite of messaging offerings was also facing growing competition from services such as Facebook Messenger, iMessage, and WhatsApp. A decision was made to scrap the existing Google Talk system and code a new messaging product through a collaboration with multiple development teams.
On February 16, 2015, Google announced it would be discontinuing Google Talk and instructed users to migrate to the Hangouts app on the Chrome browser platform.
In January 2016 Google updated the app to tell people not to use it for SMS, recommending to instead use Google's "Messenger" SMS app.
In May 2016, at Google I/O 2016, Google announced two new apps: Google Allo, an AI-based[when defined as?] messaging app and Google Duo, a video calling app. Google has since confirmed that the new apps will not replace Hangouts - Hangouts will remain a separate product.
On January 6, 2017, Google announced that the Google Hangouts API will shut down on April 25, 2017.
On March 9, 2017, Google announced that it would be evolving Hangouts into two products: Hangouts Meet and Hangouts Chat. Hangouts Meet would focus on video conferences and Hangouts Chat would be focused on instant messaging with additional features such as bot assistant and threaded messaging.
Hangouts allows conversations between two or more users. The service can be accessed online through the Gmail or Google+ websites, or through mobile apps available for Android and iOS (which were distributed as a successor to their existing Google Talk apps). However, because it uses a proprietary protocol instead of the XMPP open standard protocol used by Google Talk, most third-party applications which had access to Google Talk do not have access to Google+ Hangouts.
Chat histories are saved online, allowing them to be synced between devices. A "watermark" of a user's avatar is used as a marker to indicate how far they have read into the conversation. Photos can be shared during conversations, which are automatically uploaded into a private Google+ album. Users can also now use color emoji symbols in their messages.
As with the previous Google+ Hangouts, users can also perform a group video chat with up to 10 users at a time. In 2016 Google upgraded Hangouts to 25 concurrent users in HD video for Work/Education. The new Google Hangouts app on iOS integrates a Google Voice number to some extent, but on Android the SMS support in Hangouts doesn't fully integrate with Google Voice for calls or texts. Integration was first expected by 2014, but was deprecated in January 2016. The reason for the delay appears tied to Google switching away from the XMPP protocol it used, as mentioned above.
For Google Chrome, users do not need to install a plugin. However, for Internet Explorer 11, the user must install the "Google Talk Plugin" to be able to use the video features.
In Android 4.4, Hangouts is integrated with text messages sending and receiving functions, which is the default SMS app on the Nexus 5. For other Android phones, users can choose to open the SMS function when they download the new version of Hangouts via Google Play. SMS conversations are shown in a drawer on the left side. The update also adds GIF support and a new location-sharing button, which allows the user to send their GPS location to their contacts.
As of version 2.3 (September 12, 2014), Hangouts includes the ability to make free voice calls to other Hangouts users, and charges users (via pre-registered credit) to call landline and mobile phones internationally except for calls to the United States and Canada which are free of charge. Currently, Android users must have both the Google Hangouts and Hangouts Dialer apps installed if they wish to call landline or mobile telephone numbers via the public switched telephone network. On August 15, 2016, Google announced that Hangouts on Air will be discontinued on September 12. Users will have to utilize YouTube Live for live-streaming events.
As of May 2013, Google Hangouts faced criticism from the Electronic Frontier Foundation as they felt that Google was "moving in the wrong direction" by shrinking its support for the open standard protocol XMPP. The new protocol makes it much more difficult for multi-chat clients like Pidgin and Adium to support Google Hangouts. They must reverse engineer the protocol.
Additionally, the tight integration of Google Hangouts to Google+ can lead to the unwilling sharing of personal information to others.
As of December 9, 2015[update], Google Hangouts has a score of 2 out of 7 points on the Electronic Frontier Foundation's Secure Messaging Scorecard. It has received points for having communications encrypted in transit and for having completed a recent independent security audit. It is missing points because communications are not encrypted with keys that the provider doesn't have access to, users can't verify contacts' identities, past messages are not secure if the encryption keys are stolen, the code is not open to independent review, and the security design is not properly documented.
On November 30, 2014, Make Use Of hailed Google Hangouts as the "best messaging app on Android by far".