I was first contacted by a recruitment agency.
I had to fill out a QNR with general questions and expressing my career goals, my motivations, the reason why I wanted to work for Mandiant, strengths and flaws, activites related to InfoSec outside of work.
3 weeks later I was contacted by the HR dept for a presentation interview.
1 week later a first technical interview with the Hiring Manager (networking, security (HIDS,HIPS,)
1 week later a second one with senior analysts (more of that, in-depth questions, scenario-based, pen testing)
2 weeks later a skype interview with Hiring manager and HR.