Today there is a paradigm shift in attitude towards online education, therefore, online learning compels mathematics education to change its focus, organization and use of technology. The belief that the concept of function should be a central point in mathematics is not a recent phenomenon. Many researchers have acknowledged the difficulties students face in learning the concept of function in face-to-face class­room. On the other hand, research studies have done little to examine students' knowledge of functions and their difficulties in an online environment. Understanding students’ knowledge and difficulties with this notion in an online environment can contribute significantly to finding ways to guide students’ conceptual learning in a virtual setting. The purpose of this study was to gain insight into college students’ knowledge of functions and explore the difficulties they may have with this notion in an online learning environment. The research and the analysis put forth in this study are specifically useful for professionals in mathematics education, mathematics faculty who may be considering teaching in an online environment, and graduate students conducting research.