Contacted by a recruiting agency who asked a few questions about my resume. Followed by a phone interview with the R&D technical lead who asked some technical and behavioral questions. Invited to an on-site interview which was highly and thoroughly technical. After the on-site, did not hear back for several weeks and had to contact the recruiter to find out what was the result. Was informed that they passed on me but would keep me in mind for a potential future role. Several months later they called and asked if I was still interested. I said I was and had another round of phone interviews followed by an offer which I accepted.