Despite the growing popularity of digital teaching portfolios, research has remained focused on outcomes associated with "creating" digital teaching portfolios instead of examining how they can be used to effectively "assess" what teachers know, especially when it comes to educational technology. One barrier to using portfolios as a means of assessing teachers' knowledge of technology is the lack of a guiding framework for characterizing teachers' technology knowledge. In this paper, we propose that the Technological Pedagogical Content Knowledge (TPACK) framework is well suited to the task of studying the knowledge (including technological knowledge) teachers represent in their digital teaching portfolios. We demonstrate how the TPACK framework can guide a content analysis of digital teaching portfolios by examining 589 online portfolios created by educators as the culminating assessment in their master's studies. We conclude that the TPACK framework is helpful for analyzing the types of technological knowledge teachers may represent in portfolios but acknowledge several important challenges to its use.