Over a period of 10 years, we have developed a sustainable process of online portfolio assessment that demonstrates both reliability and validity, using both qualitative and quantitative measures. The sustainable cycle is that, each semester, we assess a random sampling of the students' work that they have posted, as per our instructions, in an online portfolio. During the reading, the faculty score the documents for 11 variables, including writing, content, audience awareness, and document design. We achieved validity by a modified online Delphi that led to a redefinition of the construct of technical communication itself; we achieved reliability by adjudication resulting in adjacent scores. The results of our assessment meet the requirements of ABET and result in a continual cycle of improvement for our technical communication curriculum. Results from three semesters show an improving correlation between the course grade and the overall, holistic portfolio score.