If you have applied to immigrate to the United States, most likely under either the family-based green card category or the employment-based green card category, you might find that you have to wait several weeks or months to hear back from the office processing your case. Most likely, that is an office of U.S. Citizenship and Immigration Services (USCIS), particularly in the early stages of the application process.
Don't panic! Such delays are normal, although certainly bothersome. At least USCIS offers various procedures by which you can check the status of your petition or application.
After you submit a petition or application to USCIS, its practice is to send a receipt, usually within several days or weeks. Look on your receipt notice for your 13-digit receipt number. The number will begin with three letters to identify the office handling the application, such as EAC, LIN, SRC, or WAC. Your receipt number will be helpful in tracing your case through the system.
If you do not receive this number after several weeks, you can call the USCIS Contact Center or make an online e-request for follow-up. If you call, USCIS might be able to resolve matters over the phone, though possibly not during the initial call; expect to be asked for a call-back number. Or, USCIS might make an appointment for you to visit a USCIS office in person.
If you are scheduled for an in-person appointment, you'll want to bring personal identification, copies of your application, and any other materials relating to your case. If you sent the application by a courier service or certified mail, bring the receipt, so that you can show the officer that you really sent it.
To get basic information about the status of your immigration application online, go to the USCIS "Case Status Online" page and enter your receipt number. It's a good idea to also sign up for case updates from USCIS by creating an account (on the same page).
Another important area of the USCIS website is the Check Case Processing Times page. There, you can find out how long the various USCIS offices or service centers are currently taking to process different types of applications and deduce whether your application has been lost in the shuffle.
If you don't have access to a computer, or have discovered that your case is taking longer than anyone else's, you can contact USCIS by telephone as described above.
Another option, if the last you know of your case is that you sent it to a USCIS lockbox (an initial processing service center, which is supposed to forward applications and petitions to USCIS service centers) is to email the lockbox using one of the address provided on the USCIS "Contact Us" page.
Keep your emails to the U.S. government polite, making sure to include all relevant facts such as the petitioner and beneficiaries' names, the date of filing, whether your filing fee check has been cashed by USCIS, and so forth.
U.S. consulates typically have less to offer in the way of online help in tracking cases, and are not consistent in how they interact with the public. You'll want to look at any correspondence you've received from the consulate for contact information, and check its website to see what it suggests regarding how to check on your case or bring up scheduling concerns.
If you're still not getting anywhere after trying the measures described above, consult an immigration attorney for help. An experienced U.S. immigration attorney can help you figure out what is happening with your case and will know what sorts of delays in processing are to be expected. In some cases, the attorneys have ways of reaching someone within USCIS that ordinary people don't.