The impostor phenomenon (IP) is an internalized feeling of fraudulence characterized by beliefs that one's personal successes are due to external factors (e.g., luck) rather than internal attributes. Individuals who suffer from impostor feelings may feel that they are not really intelligent or capable but have instead fooled others. Written descriptions of IP experiences were provided by 879 graduate and undergraduate students and submitted to content analysis. Nine major themes were identified across three categories: causes (i.e., novel experiences, challenges, everyday academic interactions, and high expectations), feelings and impact (i.e., negative psychophysiological symptoms and negative thoughts and emotions), and management (i.e., negative, neutral, and positive). Implications for addressing these feelings in post-secondary settings are considered.