Tweetmarks is a web service for setting and getting the "last read" tweet for a given Twitter user. It can be used to "sync" the reading position between multiple Twitter clients and platforms. It was created by Riverfold Software. Also see this blog post introducing the service. All Twitter client application developers: PLEASE integrate this into your clients. As for why Twitter hasn't already implemented this themselves, Marco Arment writes: Unfortunately, I doubt that Twitter’s official Mac and iOS apps will. Twitter has decided, for whatever reason, not to do this to date. I heard a while back that this was because they want people to just read what’s there now, like a river of news, not to try to “keep up” with a potentially insurmountable timeline. They didn’t want to encourage features like this that would allow someone to know how far “behind” they are, because that could cause guilt and feelings of information overload, which could discourage usage. I believe they are wrong in this line of thinking. Moving from Tweetbot on my iPhone to Twitteriffic on my iPad to the Twitter app on my Mac feels like a broken experience. Having to re-read supposed "new" updated over again to figure out my place depending on where I am just feels wrong. Twitter is arrogant in trying to dictate how users should use their service rather than trying to accommodate the reality of how their users currently use Twitter. To quote Marco again: And as long as Twitter doesn’t have an API for it, widespread Tweetmarks support in apps is badly needed for anyone who uses multiple Twitter clients. So if you make a Twitter client, please add Tweetmarks support. Yes, please.