I applied online at first, and got no answer, so I applied through a referral of a friend who works there. It seems to be that referral is the best way to go with Google.
A week later I got a response from a recruiter proposing a first phone call. I had a bit of trouble setting up the date (the Calendar invite was not working), so I just responded to the email with the time and date. The recruiter never responded, and then didn't show up or answer emails the day of the call. She then emailed me the next day with a new time, and then showed up a bit late to the call. We had the call (about 30min) and there she told me I had passed to the next round. She asked questions like "Sell Adwords to a small restaurant" and also asked about my CV and previous experience.
I had the call with the next Googler, who was a person from the Sales team. This interview was a bit harder, with questions like: "What are you passionate about? Sell that to a person who has no interest in it", or "What 3 things would you suggest to Larry Page?".
I also passed this interview, and Google offered to fly me to the office for the final round. There I had 3 interviews (total duration 2hs), regarding my analytical skills ("Calculate the potential revenue of adding Adwords to G+"), personal goals in life ("What are you passionate about"), and work experience. They had me do "difficult client situations" about 4 times ("Sell this CD player to a client" and they would be very difficult about it).
A week later, they called me and told me I passed, but I had to go through a review board. A week after they called again and said I passed that and I was offered the job.
It was an intense process, but if you study hard and read the Glassdoor reviews (very, very helpful!) then you should be ok.