Keeping abreast of new technologies and the opportunities they offer is a challenge for inservice teachers (Blake, 2008; Egbert, Akasha, Huff, & Lee, 2011; Hanson-Smith, 2006; Hubbard, 2007; Robb, 2006). An important aspect of teacher learning about the use of technology is the ability to identify the affordances of new tools and how they can support learning in the language classroom (Hampel & Stickler, 2005; Kessler, 2010). This fourteen-month-long longitudinal study of the learning of two experienced foreign language teachers working together describes how their perceptions of the affordances of two computer-mediated communication (CMC) tools developed over time. Interview data collected over three semesters demonstrated how teachers' perceptions of affordance evolve through classroom practice with technology, and how such perceptions might be transferred to the use of a new tool. As well, although the two teachers used the same tools (blogs and wikis) in the same courses and, at times, with the same classes, they perceived different learning affordances in relation to the language learning processes they prioritized. The article will conclude with suggestions for ways in which a better understanding of affordance in teacher knowledge development has implications for the support of in-service language teachers' learning.