Contrary to the common belief that expert performance is a reflection of innate abilities and capacities, this research demonstrates that expert performance in Information Systems is predominantly mediated by acquired complex skills, expertise, knowledge capabilities and experience. Analyzing data from 310 respondents representing 27 organizations, this study proposes two types of knowledge that is necessary and essential to attain expert performance in Information Systems. The relationships between the years of experience, the impact of deliberate learning of skills with expert performance are also being investigated. The study derives a classification of the ‘degree of proficiency’ for Information System key-user-groups that spans on a three-level continuum which has both practical and academic value. The study analysis of the degree of proficiency provides empirical evidence on the potential and limits of environmental adaptation and learning.