This study examined how instructional design (ID) experts used their prior knowledge and previous experiences to solve an ill-structured instructional design problem. Seven experienced designers used a think-aloud procedure to articulate their problem-solving processes while reading a case narrative. Results, presented in the form of four assertions, showed that experts (1) narrowed the problem space by identifying key design challenges, (2) used an amalgam of knowledge and experience to interpret the problem situation, (3) incorporated a mental model of the ID process in their problem analyses, and (4) came to similar conclusions about how to respond to the situation, despite differences in their initial conceptualizations. Implications for educating novice instructional designers are discussed. (Contains 2 tables.)