The purpose of the present thesis was to extend knowledge of the impact of implicit affect in the process of effort mobilization. The implicit-affect-primes-effort model (Gendolla, 2012, 2015) makes specific predictions and gives explanations for the influence of implicit affect on effort mobilization. Briefly, the IAPE model posits that implicit affect influences effort through its impact on subjective demand, which in turn influences effort according to the principles of motivational intensity theory (Brehm & Self, 1989). The present thesis focused on implicit fear, which is an implicit affect that was not studied to date. Based on the IAPE model (2012, 2015) implicit fear should activate the difficulty concept, which should increase experienced task demand and in turn determine effort mobilization according to the principles of motivational intensity theory (Brehm & Self, 1989). We conducted four studies to test these predictions.