What is the Selection Process at Microsoft?

1st one. Your CV is reviewed and matched the job requirements. This is the shortest round and you may be contacted within a week with the second round interview proposition.
2nd round appeared to be the longest one. Generally you will talk to different people on the phone. You'll be asked technical questions and tested in different aspects like basic knowledge, background depth, logical thinking, etc. Finally your team player skills will be tested by the HR department in 30-45 minutes call. Since HR is the one who makes the decision whether you match the requirements you'd better stay focused during this call and answer exactly what is asked. Do not inventing anything. Be honest. When this round is over you'll be contacted in a few weeks with the outcome. 
3rd round is mostly technical. You'll be invited to talk face-to-face with Microsoft employees. Some of them ask algorithms, some asked me to test the function and a few people came with their problems in projects  them sort the problems out.