The pursuit of happiness is a central goal for many people, yet scientific research on how to increase and sustain happiness has been limited due to pessimism from genetic determinism and hedonic adaptation. However, emerging optimism suggests that happiness can be permanently increased. The authors propose that chronic happiness is influenced by three factors: a genetically determined set point, happiness-relevant circumstances, and happiness-relevant activities. Activities offer the best opportunities for sustainable happiness increases. Research supports this model, including preliminary happiness interventions. Happiness is defined as frequent positive affect, high life satisfaction, and infrequent negative affect. It is influenced by genetic, circumstantial, and intentional factors. The set point, or genetic baseline, is stable and difficult to change. Circumstances, such as income and health, have limited long-term impact due to hedonic adaptation. In contrast, intentional activities, such as gratitude practices or goal pursuit, can lead to sustained happiness increases. These activities are more effective because they are not subject to adaptation, as shown by longitudinal studies. Intentional activities are episodic, varied, and can be tailored to individual needs. They help combat adaptation by providing fresh experiences and maintaining engagement. For example, practicing gratitude or engaging in meaningful goals can enhance well-being. Research shows that people who pursue self-concordant goals experience greater well-being. Additionally, intentional activities can be maintained over time, as demonstrated by studies showing that students who continue to achieve their goals maintain higher well-being. The distinction between life circumstances and intentional activities is crucial. While circumstances are external and subject to adaptation, intentional activities are chosen and can be adjusted to maintain their effectiveness. This makes intentional activities a more promising avenue for sustainable happiness. However, maintaining these activities requires consistent effort and commitment. Overall, the model suggests that intentional activities offer the best potential for increasing and sustaining happiness, especially after basic needs are met.The pursuit of happiness is a central goal for many people, yet scientific research on how to increase and sustain happiness has been limited due to pessimism from genetic determinism and hedonic adaptation. However, emerging optimism suggests that happiness can be permanently increased. The authors propose that chronic happiness is influenced by three factors: a genetically determined set point, happiness-relevant circumstances, and happiness-relevant activities. Activities offer the best opportunities for sustainable happiness increases. Research supports this model, including preliminary happiness interventions. Happiness is defined as frequent positive affect, high life satisfaction, and infrequent negative affect. It is influenced by genetic, circumstantial, and intentional factors. The set point, or genetic baseline, is stable and difficult to change. Circumstances, such as income and health, have limited long-term impact due to hedonic adaptation. In contrast, intentional activities, such as gratitude practices or goal pursuit, can lead to sustained happiness increases. These activities are more effective because they are not subject to adaptation, as shown by longitudinal studies. Intentional activities are episodic, varied, and can be tailored to individual needs. They help combat adaptation by providing fresh experiences and maintaining engagement. For example, practicing gratitude or engaging in meaningful goals can enhance well-being. Research shows that people who pursue self-concordant goals experience greater well-being. Additionally, intentional activities can be maintained over time, as demonstrated by studies showing that students who continue to achieve their goals maintain higher well-being. The distinction between life circumstances and intentional activities is crucial. While circumstances are external and subject to adaptation, intentional activities are chosen and can be adjusted to maintain their effectiveness. This makes intentional activities a more promising avenue for sustainable happiness. However, maintaining these activities requires consistent effort and commitment. Overall, the model suggests that intentional activities offer the best potential for increasing and sustaining happiness, especially after basic needs are met.