I applied online. The process took 4 months. I interviewed at Library of Congress (Washington, DC) in July 2017
Interview
Structured questions that matched the job posting exactly. They will likely take notes, won't look at you and possibly won't elaborate much. They have a script to follow. If you're curious, you can FOIA their notes.
Interview questions [1]
Question 1
Tells us a time you have to work with a difficult person.