CAN and COULD have multiple uses and multiple interpretations, which can be difficult for learners of English to understand. For example, the difference of "Can you help me?" and "Could you help me?" may go unnoticed to an English language learner, but a native speaker of English would recognise a difference in politeness. The current paper reports on an investigation of learners' use of the modal auxiliaries CAN and COULD, including their negative counterparts ("cannot/can't" and "could not/couldn't"), in an English Proficiency Program (EPP) classroom at a New Zealand University. Through first examining the learners' use of CAN and COULD in spoken and written contexts, comparisons are made to their use in the "British National Corpus", which results in the identification of areas in which learners' use could be strengthened.