Purpose: To examine the influence of individual participant, instructor, and group factors on participants’ attendance and adherence to community exercise classes for older adults. Design and Methods: Longitudinal data from 16 instructors, 26 classes, and 193 older participants within those classes (aged 60–100 years) were examined. Data were collected using questionnaires on individual participants’ demographics, attitudes, health perceptions and conditions, and group cohesion. Instructors’ demographics, training, background, experience, attitudes, and personality were collected. Group factors included class type, cost, transport, and whether the class was held in an area of deprivation. Outcomes (attendance/adherence) were collected through attendance records. Results: Multilevel modelling (MLwiN) revealed both instructor and individual participant variables were important in understanding attendance and adherence. Individuals’ housing, education, mental well-being, group cohesion, and attitudes were important predictors of attendance at 3 and 6 months. Instructors’ age, gender, experience, and motivational training were important at 3 months, whereas instructor personality was important at both 3 and 6 months. Having attended longer than 6 months at baseline, participants’ attitudes, weeks offered, instructors’ personality, and experience were associated with adherence at 6 months. Implications: Results suggest that instructors’ characteristics alongside individual participant factors play a role in influencing participants’ attendance to exercise classes. These factors should be considered when setting up new programs.