Twitter question... when someone sends you a direct message that's not following you, why can't you direct message them back?

Twitter is a service for friends, family, and co–workers to communicate and stay connected through the exchange of quick, frequent messages. People write short updates, often called "Tweets" of 140 characters or fewer. These messages are posted to your profile, sent to your followers, and are searchable on Twitter search.

Do I need anything special to use it? All you need to use Twitter is an internet connection or a mobile phone. Join us here!

Once you're in, begin finding and following accounts whose Tweets interest you. We'll recommend great accounts once you're signed up. How do I find people to follow?

When you create an account, you can search for people by name or user name, import friends from other networks, or invite friends via email. You can also follow some of the people we've suggested. What does it mean to follow someone on Twitter?

Following someone means you've chosen to subscribe to their Twitter updates. When you follow someone, every time they post a new message, it will appear on your Twitter home page. Read more here.

How do I know who I'm following? After you click the 'Follow' button on someone's profile, you're following them. See a list of people you're following by clicking on the following link on your profile page or on your home page's sidebar.

How do I know who is following me? Twitter sends you an email when someone new follows you. Set up your email preferences to notify you when you have a new follower.

The 'Followers' link on your profile page or home page's sidebar will also tell you who is following you. What are follow limits? Twitter has follow and update limits for stability and abuse control.

You can read more about this here. Who reads my updates? Your followers read your Tweets.

If your Tweets are public, anyone who runs a search for a keyword in your Tweet may be able to see that message. Your Tweets are public by default; if you're hesitant to have people you may not know read your updates, protect your Tweets to approve followers and keep your updates out of search. Can I block people from following me?

Yes, you can. If you block someone, they won't be able to follow you or send you any messages. Read more here.

How can I send updates to Twitter? Read our article about how to post a Tweet. You can tweet from twitter.com, from your phone, or from an application.

Can I put my Twitter updates on my blog? Put a Twitter widget on your blog or website – anywhere that accepts Javascript or HTML. What are @replies?

If a message begins with @username, meaning it was directed to another user, it is an @reply. Click the Reply button on another person's Tweet to reply to it. Please note that if your Tweets are protected, users who are not following you will not see your @replies or mentions.

Read more here. What are direct messages? Direct messages are personal messages sent from one Twitter account to another; they do not appear in public for anyone else to read.

You can only send a direct message to a person who follows you. Read more here. What is the difference between an @reply and a direct message?

An @reply is a public message sent regardless of follow-ship. Anyone can view it (if your Tweets are public). A direct message can only be sent by someone you follow, and can only be seen by the sender and intended recipient.

Can I edit a Tweet once I've posted it? Once a Tweet has been posted, it can't be changed. You can delete an Tweet by clicking the trash icon on the right end of it.

What's a Retweet (RT)? A retweet is a re-posting of someone else's Tweet. Read more here.

Why can't I see all my Tweets? Are they lost? We store all your Tweets.

You can click the Me tab to view up to 3200 of your most recent Tweets in your profile timeline. To view more, you can download your Twitter Archive and browse a snapshot of your Twitter information, starting with your first Tweet. How do I post a picture to Twitter?

Uploading and sharing images on Twitter.com is easy! You can find step-by-step instructions and more FAQ here. Is there a Twitter API?

Yes, complete with documentation and an active developer group to help you with common API questions. Find our more at dev. I'm an app developer, how do I get whitelisted?

Get more information here on what API access you may need, and how to request whitelisting. Does Twitter allow HTML in Tweets? We escape all HTML for security purposes.

If you paste in a link that is less than 30 characters, we'll post it in its entirety. If it's longer than 30 characters, we'll convert it to a shorter URL. How do I report spam?

We have a whole article about how to report spam on Twitter. Please read it. We encourage you to always block any spammers you find.

Why are accounts suspended? Accounts are suspended for Terms of Service violations or spam investigation. Read more about this here.

Where can I find out more information about Twitter's Terms of Service? Twitter's Terms of Service is posted on the website, and the Twitter Rules are posted in the Help Center. How do I submit a complaint about copyright, impersonation, trademark, or other Terms of Service issues?

Review our Terms of Service section to find out what constitutes a violation, and how to go about fixing a related problem. Is there a place where I can find out if there are problems with Twitter? Check the Something's Not Working section, read the Twitter Status Blog, or follow @support.

Still wondering about something? Try using the search box in the blue bar at the top of this page, or browse our Help Center. Check out our Troubleshooting section for solutions to common problems.