This descriptive analysis illustrates some of the challenges in measuring investment in professional development and concludes by highlighting a promising strategy using online data systems that might improve the accuracy of spending estimates and the tracking of expenditures. Previous literature defines two categories of professional development: traditional professional development, such as workshops, conferences, and college courses for credit, and integrated professional development, such as teacher collaboration during common planning periods, teacher mentoring, academic coaches, observation of others, and individual research projects. This study adapts the conceptual framework established by Odden et al. (2002) to derive cost estimates of professional development in the sample districts. Data sources were identified for six districts in four states in the Southwest Region to determine how much these districts were spending on professional development. Before initial contact with the targeted districts, state and district policies and practices likely to influence investment in professional development were investigated. The four states covered by this study require districts to develop formal plans for implementing professional development. These planning documents were obtained from the six districts in advance of data collection and helped identify the potential financial implications of implementing professional development. The framework from Odden et al. (2002) was used to identify data sources that could estimate the six districts' total investment in professional development and disaggregate the total by object of expenditure , function, and source of funding. Based on these six districts' data, an estimated 2-9 percent of district spending was allocated to professional development activities. As with previous studies, this may underestimate investment because of the difficulty of obtaining accurate data on professional development that is more integrated into the daily and weekly work of teachers. Future research could explore how feasible online systems would be for obtaining more accurate data on the time allocation of education professionals to better estimate the cost of professional development. Three appendixes are included: (1) Recruitment of Districts in the Study's Sample; (2) Cost Analysis Framework; and (3) Policies and Characteristics of State and District Professional Development. (Contains 13 notes, 2 boxes, and 7 tables.) [This report was prepared for the National Center for Education Evaluation and Regional Assistance, Institute of Education Sciences (IES) by Regional Educational Laboratory Southwest administered by Edvance Research, Inc.]