Are you still being considered? When should you expect to hear from them, if ever? Is it OK to check in and ask?
While in general it's best not to nag employers to respond to you, there are times when it's OK to check in and see where your application stands. The rules are different, though, depending on whether you've simply submitted an application or you've been interviewed.
After You Submit Your Application
It can be tempting to contact the employer after you've submitted your application and ask where things stand. But while it's an understandable question, it's best to resist the temptation to ask, at least for a while. Once you've submitted an application, the ball is in the employer's court. It might take them a while to sort through applications (and they may not even start that process until weeks after you sent yours in), but they'll get in touch if they want to talk with you.
If you absolutely must follow up at this stage, wait at least two weeks after applying, and then send a short email saying something like this: "I recently applied for your __ position, and I just wanted to reiterate my strong interest. I think it might be a great match, and I'd love to talk with you about it when you're ready to begin scheduling interviews."
Note that you're not asking for a response—you're simply highlighting your interest. That's because most employers don't like to field follow-up questions before they've even decided if you're a strong candidate, and it's not good to annoy employers at this stage. Note, too, that you should use email for this rather than calling, for the same reason.
If a month has passed and you haven't heard anything, assume that you're not being considered and mentally move on. It's still possible that the employer might contact you, but you're better off not agonizing about it and instead putting it out of your mind.
After a Job Interview
The first thing to do is to realize that it may take a while to hear something after your interview, even if you felt like you had momentum. Hiring often takes much longer than applicants expect— and even longer than the employers themselves expect, and employers are notorious for leaving applicants hanging after interviews.
The best thing you can do is to end your interview by asking what the employer's timeline is for next steps. If you do that and that time passes, then you have a perfect opening to follow up with a quick email, explaining that you remain very interested in the job and asking if they have an updated timeline.
But if you didn't remember to ask that at the end of your interview, then within a week or two of your last contact, it's fine to send a short email asking when they're likely to move forward with next steps.
Keep in mind here that you're not so much asking for the status of your application as you're simply asking about the timeline for next steps. The reason for that is that they might not be able to give you an answer about your "status"—they might be waiting for feedback from other interviewers, or waiting to meet with other candidates, or a decision-maker might be out of town, or the person you're asking might simply not know. Or, the company might have a policy of not notifying candidates about their status until final decisions have been made. As a result, this type of query can lead to you getting no response, or a response that isn't useful. So instead, ask about the timeline; that's a query that's easier to respond to with information that you'll find useful.
Alison Green writes the popular Ask a Manager blog, where she dispenses advice on career, job search, and management issues. She's also the co-author of Managing to Change the World: The Nonprofit Manager's Guide to Getting Results, and former chief of staff of a successful nonprofit organization, where she oversaw day-to-day staff management, hiring, firing, and employee development.