Most educators are familiar with instances of authentic assessment of "content" within the disciplines or of authentic assessment of "discipline-specific skills." In such authentic assessments, students apply the knowledge and skills of the discipline to situations or tasks that replicate real world challenges. The measurement of skills is particularly well suited to authentic assessment because meaningful demonstration of skill acquisition or development requires a performance of some kind. Yet, one rarely assesses, authentically or otherwise, the critical "cross-curricular or process skills" such as self-assessment, information literacy, collaboration, or metacognitive skills. Nevertheless, these critical skills definitely can and should be assessed. To explain how, the author describes the "summative" assessment of skill development, that is, "final" judgments of whether or not a skill has been acquired and can be applied. (Contains 4 figures.)