A many-faceted Rasch model (FACETS) is presented for the measurement of writing ability. The FACETS model is a multivariate extension of Rasch measurement models that can be used to provide a framework for calibrating both raters and writing tasks within the context of writing assessment. A FACETS model is described based on the current procedures of the Georgia Basic Skills Writing Test. These procedures can be seen as a prototype for other statewide assessments of writing. A small data set produced by 15 eighth grade students from this assessment is analyzed with the FACETS computer program of J. M. Linacre (1988). The FACETS model offers a promising approach for solving a variety of measurement problems in the statewide assessment of writing ability. It provides a framework for obtaining objective linear measurements of writing ability that generalize beyond specific raters and writing tasks. The FACETS model can also be applied to the assessment of writing ability based on holistic scoring and exploration of issues related to bias. A 37-item list of references, 5 tables, and 2 figures are included. (SLD)