Successfully interviewed for 3 positions: Intern, Program Assistant, then Program Officer. The latter were both from an internal perspective.
I interviewed for a summer internship (paid). Began with a call with HR outlining the company, department, and position with expected pay. Then moved on to the skype interview (I was out of the state) with 2 managers and 3 analysts.
The Program Assistant and Program Officer positions interview processes were similar with a call with HR and then an in-person interview.
For the intern and Program Assistant positions I knew someone in the department. This helps a lot at FHI and in DC in general, it gets your resume to the top and someone to vouch for you.