Drawing on the play and work design literatures, we conceptualize and validate an instrument to measure playful work design (PWD) – the proactive cognitive-behavioral orientation that employees engage in to incorporate play into their work activities to promote fun and challenge. Across three studies (N=1006), we developed a reliable scale with a two-dimensional factor structure. In Study 1, we utilized expert-ratings and iterative exploratory factor analyses to develop an instrument that measures (1) designing fun and (2) designing competition. Additionally, Study 1 evidences the divergent and convergent validity of the subscales as well as their distinctiveness. Specifically, PWD was indicative of proactivity as well as play, and designing fun especially correlated with ludic traits (i.e., traits focused on deriving fun; e.g., humor), whereas designing competition particularly correlated with agonistic traits (i.e., traits focused on deriving challenge; e.g., competitiveness). Study 2 cross-validated the two-factor structure, further investigated the nomological net of PWD, and revealed that PWD is distinct from job crafting. Finally, Study 3 examined the predictive and incremental validity of the PWD instrument with self- and colleague-ratings two weeks apart. Taken together, the results suggest that the instrument may advance our understanding of play initiated by employees during work.