This study sought to generate a more robust understanding of teacher (in)authenticity. In other contexts, authenticity is regarded as a display of true self and has been positively linked to beneficial psychological (e.g., increased self-esteem) and social outcomes (e.g., higher relational satisfaction). However, what it means to be authentic in relational contexts may be very different from what it means to be authentic in teaching. Indeed, the concept of authentic teaching has been discussed by many, but has yet to be examined from a social science perspective. Using a grounded theory approach, this study sought to determine student perceptions of both authentic and inauthentic teacher behavior and communication. Open-ended data from 297 college students indicate that there are distinct behaviors employed by (in)authentic teachers. Results indicated that authentic teaching is perceived when teachers are viewed as approachable, passionate, attentive, capable, and knowledgeable. Alternatively inauthentic teaching is observed when teachers are perceived as unapproachable, lacking passion, inattentive, incapable, and disrespectful. Notably, these behaviors are often demonstrated through distinct actions taken by teachers that are often examined within the larger instructional communication literature (e.g., self-disclosure). Practically, these results allude to the notion that (in)authentic teaching can have a meaningful impact on students.