In the current study we aim to test the effects of implementations and planfulness on goal-directed behavior. Individuals scoring high and low on a brief pre-screen measure of planfulness will be eligible to participate. Equal numbers of high- and low-planfulness participants will be randomly assigned to an experimental condition in which they will receive messages prompting them to form an implementation intention to respond to a critical number in a subsequent ‘go no-go’ decision-making task, or a control condition in which they will receive a message prompting them to perform an alternative ‘familiarisation’ exercise with reference to the critical number. Participants will then engage in the go no-go task in which they will be required to respond to numbers via a key press and withhold their response to letters. Reaction times to a critical number, controlled for reaction times to non-critical numbers, will be the dependent measure of task peformance. Consistent with our theory, we predict an interaction effect of planfulness (low vs. high planfulness) and planning (implementation intention vs. familiarization) conditions on task performance. We also expect main effects of implementation intentions and planfulness on performance, although these should be qualified by the interaction effect.