I was first called via phone shortly after I applied for a phone interview. Basic questions regarding past experience, how I heard about the company, etc. They asked me to come in for an assessment, which was skill related geared towards typing skills, personality, and other grammatical skill.
About a week after the assessment, I was called in for a 1:1 interview, in which the interviewer asked more in depth questions regarding me as a person, mostly not related to my skills. Culture is very important to Wayfair, and they only hire people that they feel will blend nicely with the type of company that Wayfair is.