This meta-analysis examines the effectiveness of implementation intentions—specific if–then plans that specify when, where, and how to act in pursuit of a goal—in promoting goal achievement. Findings from 94 independent studies show that implementation intentions have a medium-to-large effect size (d = .65) on goal attainment. They are effective in promoting the initiation of goal striving, shielding ongoing goal pursuit from unwanted influences, disengaging from failing courses of action, and conserving capability for future goal striving. Implementation intentions also enhance the accessibility of specified opportunities and automate goal-directed responses. Goal intentions, which are self-instructions to achieve outcomes or perform behaviors, are typically formed through beliefs about the feasibility and desirability of actions. However, research suggests that goal intentions alone are not sufficient to ensure goal achievement, as people often fail to translate intentions into action. This is partly due to factors such as forgetting to act, failing to seize opportunities, initial reluctance to act, and being derailed by distractions or conflicting goals. To address these challenges, implementation intentions provide a strategy for effective self-regulation of goal striving. They involve forming specific plans that link good opportunities to act with effective responses. Implementation intentions can be distinguished from goal intentions by specifying both the behavior and the situational context in which it will be enacted. The component processes of implementation intentions include increased accessibility of critical cues, spontaneous attention to cues, and the automation of goal-directed responses. These processes are supported by evidence showing that implementation intentions enhance cue detection, attention, and recall. They also exhibit features of automaticity, such as immediacy, efficiency, and lack of conscious intent. Overall, implementation intentions are a powerful strategy for enhancing goal achievement by bridging the intention–behavior gap and facilitating effective self-regulation of goal striving.This meta-analysis examines the effectiveness of implementation intentions—specific if–then plans that specify when, where, and how to act in pursuit of a goal—in promoting goal achievement. Findings from 94 independent studies show that implementation intentions have a medium-to-large effect size (d = .65) on goal attainment. They are effective in promoting the initiation of goal striving, shielding ongoing goal pursuit from unwanted influences, disengaging from failing courses of action, and conserving capability for future goal striving. Implementation intentions also enhance the accessibility of specified opportunities and automate goal-directed responses. Goal intentions, which are self-instructions to achieve outcomes or perform behaviors, are typically formed through beliefs about the feasibility and desirability of actions. However, research suggests that goal intentions alone are not sufficient to ensure goal achievement, as people often fail to translate intentions into action. This is partly due to factors such as forgetting to act, failing to seize opportunities, initial reluctance to act, and being derailed by distractions or conflicting goals. To address these challenges, implementation intentions provide a strategy for effective self-regulation of goal striving. They involve forming specific plans that link good opportunities to act with effective responses. Implementation intentions can be distinguished from goal intentions by specifying both the behavior and the situational context in which it will be enacted. The component processes of implementation intentions include increased accessibility of critical cues, spontaneous attention to cues, and the automation of goal-directed responses. These processes are supported by evidence showing that implementation intentions enhance cue detection, attention, and recall. They also exhibit features of automaticity, such as immediacy, efficiency, and lack of conscious intent. Overall, implementation intentions are a powerful strategy for enhancing goal achievement by bridging the intention–behavior gap and facilitating effective self-regulation of goal striving.