This policy brief presents a strong case for the creation of a statewide teacher data system in California by highlighting some of the simple teacher workforce questions that cannot be answered because such a system does not currently exist. At the state level, data on teacher qualifications are needed to fulfill the new reporting requirements of the federal No Child Left Behind Act (NCLB) and the recent Williams lawsuit settlement. At the county and district levels, local officials need reliable data to monitor the match between teachers' assignments and their credentials, understand what attracts teachers to the profession, and determine what contributes to their decision to leave it. State and local decision-makers need good data on the make-up of the K-12 teacher workforce. But in order to get this information, the state's teacher data system needs to be redesigned. The existing system also makes it difficult for local education agencies to compile data for reporting required under NCLB. This policy report pinpoints two primary and related problems representing deficiencies of California's available data: (1) Fragmented responsibility for collecting and reporting teacher data; and (2) Lack of a commonly used unique teacher identifier to allow linkage across data systems. The Center for the Future of Teaching and Learning offers the following seven recommendations: (1) A common identifier, such as teacher Social Security Number (SSN) or another unique teacher identifier should be used by all relevant agencies to enable longitudinal analysis and linkage across datasets; (2) An independent organizational structure should be adopted at the state level to oversee the teacher data system and ensure accuracy, validity and appropriate access over time; (3) Data collected by different agencies and/or organizations such as CCTC, CDE, STRS and statewide teacher programs should be merged on a regular, timely basis; (4) Analyses of the data in the teacher data system should be performed annually on a specified time line and made available to policy-makers and the public; (5) Measures to ensure access to the data for legitimate research should be established; (6) A regular system of accounting for data accuracy should be established to ensure that data and subsequent analyses are reliable; and (7) Standards should be developed and used across all involved agencies to protect teacher privacy and ensure appropriate uses of the data system for the purposes of evaluating programs and policies. The brief concluded by noting that an overhaul of California's teacher information system is long overdue. NCLB has presented the state with an opportunity to rethink the current system and redesign it to meet new federal reporting requirements.