All of us are familiar with search as users. And as software engineers, many of us have worked on search problems in the context of web search, site search, or enterprise search. But search at LinkedIn is different. Our corpus is a richly structured professional graph comprised of 364M+ people, 3M+ companies, 2M+ groups, and 1.5M+ publishers. Our members perform billions of searches (over 5.7B in 2012), and each of those searches is highly personalized based on the searcher's identity and relationships with other professional entities in LinkedIn's economic graph. And all this data is in constant flux as LinkedIn adds more than 2 members every second in over 200 countries (2/3 of our members are outside the United States). As a result, we've built a system quite different from those used for other search applications. In this talk, we will discuss some of the unique challenges we've faced as we deliver highly personalized search over semi-structured data at massive scale.