A job analysis was conducted to define knowledge important for entry-level middle school mathematics teachers. The results will be used to guide the development of new test content specifications for The Praxis Series Middle School Mathematics assessment. A draft domain was constructed from national standards, professional organization standards and current test specifications. A national advisory committee (NAC) of middle school mathematics teachers and college faculty reviewed and modified the draft domain to reflect the knowledge they believed was important for safe and effective practice and needed at time of entry into the profession. The revised domain consisted of 32 statements clustered within five major categories: (a) Numbers and Operations, (b) Algebra, (c) Functions and their Graphs, (d) Geometry and Measurement and (e) Probability, Statistics, and Discrete Mathematics. Survey responses of 575 middle school mathematics educators provided independent evidence of the importance of the domain. Respondents judged each knowledge statement on a scale ranging from 1 (not at all important) to 5 (extremely important). A total of 31 knowledge statements had mean ratings above 3.50 in the aggregate sample and for subgroups containing more than 30 respondents. The results indicate that these 31 statements may be considered appropriate for guiding the development of new test content specifications for the Praxis Middle School Mathematics assessment.