An Ironman triathlon, which consists of swimming 2.4 miles, biking 112 miles, and running 26.2 miles, requires extensive training with planned recovery to prevent overtraining. Prior to a race, athletes commonly take a period of time for reduced training, known as a taper. Although much is known about the physical benefits of a taper, little is known about the psychological changes that occur in athletes during taper. This study assessed the mood and athletic engagement (AE) of triathletes during Ironman training, tapering, and post-race, with specific attention paid to these variables during taper. Nineteen participants, who were training for one of three selected late-season Ironman races, were recruited for the study. Data were analyzed for eight participants (five males and three females, Mage data for all time points: training, taper, and post-race. Mood subscales of the Brunel Mood Scale (Terry et al., 1999) and an overall mood scale, as well as the Athlete Engagement Questionnaire (Lonsdale et al., 2007), assessed weekly mood and engagement, respectively. Data were analyzed using time series regression analysis. Results showed no overall trends in change of mood and engagement across the three time points. However, there were significant changes in several variables on an individual level during the taper and post-race period. These individual changes demonstrate that psychological reaction to taper is a personal experience, and factors such as goal orientation, goal satisfaction, social support, competence, and coping strategies can impact the training, tapering, and post-race experience.