Poor graduate throughput and industry feedback on graduate inability to cope with the complex knowledge practices in twenty-first century engineering "problem solving" have placed pressure on educators to better conceptualise the theory-practice relationship, particularly in technology-dependent professions. The research draws on the social realist work of Basil Bernstein and uses the Legitimation Code Theory dimension of Specialization to interrogate different disciplinary organising principles and their impact on complex sociocultural practices. Data gathered from 18 engineering case studies situated in three different types of industrial practice sites form the empirical basis of the original study. This paper focuses on the application of a Language of Description to aspects of the problem-solving process which illuminate the nature of disciplinary knowledge in practice. The intention is to provide educators across professions with empirical insights into the theory-practice relationship in a complex problem-solving context, and which might inform their curriculum and pedagogic design thinking.