Mrs is a lightweight but high performance implementation of the MapReduce programming model for parallel computation. It is optimized for computationally intensive programs, especially those which are iterative, though it is applicable to a wide range of applications. It is intended to be simple to install and use. It is written in Python, supports both Python 2 and Python 3, and has no dependencies outside the standard library. The name "Mrs" derives from the practice of referring to MapReduce programs by the title "mister" (e.g., "Mr. Wordcount").