Background: Positive psychology interventions have been shown to increase happiness and well-being, and researchers are beginning to speculate on the mechanisms through which these interventions may be effective, such as positive emotion, behavior and thought. Short interventions matched to an individual’s current context may be a route to boosting positive emotion in everyday life contexts where people have limited time.Methods: In the first study 250 UK participants completed a control task or three short tips selected from a list of 10. Positive emotion was monitored before and 15 minutes after the task via PANAS (Positive and Negative Affect Schedule) and additional items in a new Positive Emotional Intensity Scale (PEIS). Study 2 was a series of user centered design sessions with 18 UK participants to identify the key design principles for a Smartphone App intervention to boost positive emotion in an everyday life context. Study 3 involved 280 UK participants who either used the Smartphone App for two days or were in a control group. PANAS and PEIS were monitored during the intervention period and two days before. Personality, Adult Playfulness and the Satisfaction with Life Scale were deployed as potential moderators. The fourth study followed a similar design to study 1 but with 406 Chinese participants completing the short tips translated into Chinese, with PANAS, PEIS and Flourishing monitored before and after.Results and Discussion: In Study 1, we found three short tips increased positive emotion, relative to the control, as monitored by PEIS (but not PANAS). Study 2 identified twelve design principles that were used to develop the Smartphone App, which delivers short tips tailored to an individual’s context. Study 3 found that the Smartphone App boosted positive emotion (PEIS) and reduced PANAS Negative Affect relative to a control. In study 4 the same tips used in study 1 also increased positive emotion for Chinese participants when monitored via PANAS (but not PEIS).Conclusions: Varied short tips to boost positive emotion, behaviors and thoughts, which are matched to an individual’s context, may be an effective approach to enhancing happiness and well-being.