Zillow, the leading real estate and rental marketplace in USA, uses R to estimate home values (Zestimates) and rental prices (Rent Zestimates). Every day, we refresh Zestimates and Rent Zestimates on Zillow.com for more than 100 million homes with output from scoring daily re-trained models. The model training and scoring infrastructure rests on top of R, allowing rapid prototyping and deployment to production servers. We make extensive use of R, including the development of an in-house package called ZPL that functions similar to MapReduce on Hadoop, but runs on relational databases. In this presentation, we will go under the hood to see parts of the engine that power the Rent Zestimates.