Fast growth means lots of hiring. And there was a lot of hiring at Amazon. At many times, I was doing 1-3 interviews every day.
Different people had different interview techniques. I spent a lot of time refining mine. I did much reading on different strategies, tried borrowing ideas from Microsoft and elsewhere, and pulled other Amazonians into long discussions and debates about hiring.
In the end, I settled on looking for three things: enthusiasm, creativity, competence.
On enthusiasm, I wanted to see that the candidate had done at least minimal research into Amazon, the business, and the website. I was shocked by how many people came in to interview at Amazon who had never used the website. Here you are, considering spending the next few years at Amazon, and you didn't do some basic investigation beforehand? C'mon, that's just lame.
On creativity, I usually looked for ideas on how to improve the site. It didn't matter if we had already thought of the ideas. I realize how hard it is to come up with cool ideas from the outside. But I wanted to see some exploration of how things could be done better.
On competence, I merely attempted to verify what they said on their resume. If they claimed to be an expert in C++, could they answer a couple introductory level questions about C++? If they claim to know Python, can they write a trivial 5-10 line program in Python? If they have a degree in computer science, can they talk about algorithms and data structures? On some project they said they did in the past, can they talk about it in depth and with enthusiasm for all the little details?
By the way, exploring someone's knowledge doesn't necessarily require knowledge of it yourself. You can just keep asking questions, diving deeper and deeper. If they really understand the problem, they should be able to explain it to others, to teach people about the problem.
Eventually, you should get to a point where they say "I don't know" to a question. That's a great sign. Knowing what you know isn't as important as knowing what you don't know. It is a sign of real understanding when someone can openly discuss where their knowledge ends.
Reading over these questions now, it may sound like an easy filter. Minimal enthusiasm for and research of Amazon.com, a couple creative ideas on improving Amazon, and don't lie or exaggerate on your resume. Wouldn't everyone pass that?
As it turns out, no. Offhand, I'd guess that I rejected about 90% of candidates during phone screens and another 90% during face-to-face interviews. A filter for enthusiastic, creative, competent people seemed to be a surprisingly harsh one.
Of these three things, I think the single biggest predictor of success at Amazon.com was enthusiasm.
Amazon was a chaotic environment. Getting things done required initiative. Amazon needed people who would grab problems by the throat and never let go. Part of my work every day was to find them.