Athletes can facilitate optimal performance using emotion regulation (ER) strategies to influence the emotions they experience and how these emotions are expressed (Beatty & Janelle, 2020). The Athlete Emotion Regulation Strategies Scale (AERSS) is a new measure to assess athletes' typical use of ER strategies. This presentation covers the scale development process and the procedures used to establish item-content relevance evidence of validity using a panel of experts (comprised of practitioners and academics). Aiken's V assessed items' loadings onto keyed domains. Forty-two (86%) items had significant Aiken's Vs, indicating items related strongly to keyed domains. Estimate sizes (ES) assessed the magnitude of differences of item ratings on keyed and non-keyed domains. Due to a lack of covariance of ratings for multiple items (k = 99) an ES could not be calculated, so in these instances mean differences between keyed and non-keyed domains were examined instead. Differences ? 2.50 were considered large effects. Aiken's H assessed degree of agreement among experts of items on keyed and non-keyed domains. Values ranged from 0.10 to 1.00 (M = .54 ± .20), indicating moderate agreement among raters of items on keyed domains. The significant Aiken's V, H, and magnitude of ES's justify retaining 33 items of the original 50. Retained items are purported to represent four domains informed by the Process Model of Emotion Regulation (Gross, 2015): Up-regulating Pleasant Emotions (n = 9), Down-regulating Pleasant Emotions (n = 9), Up-regulating Unpleasant Emotions (n = 7), and Down-regulating Unpleasant Emotions (n = 8).