Objective: To investigate if divorced parents celebrate their children's birthdays with their respective ex-partner and current partner, and whether they do so "jointly" with both. Background: Family rituals like birthday celebrations are important and meaningful events in people's lives, but little is known about who partakes in these in contemporary postdivorce families. Method: We assessed whether divorced parents celebrated their child's birthday together with their ex-partner (i.e., the child’s other biological parent), current partner (i.e., the child’s stepparent), and jointly with both. Dutch Data (N=2,451) was analyzed using linear probability models. Results: Most parents celebrated the child's birthday without the ex-partner, but with the current partner. One quarter celebrated with both. The ex-partners' presence was more likely when parents' and their current partners' relationship with the ex-partner was good; and less likely when parents had repartnered and when the ex-partners had sole custody or additional biological or stepchildren. The presence of the current partner was more likely in case of coresidence with the biological parent and when the ex-partner had a new partner; and less likely when the ex-partners had sole custody and when parents' relationship with the ex-partners was good. Conclusion: Child-related family rituals mostly involve the "new" stepparent rather than both biological parents. The effects of relationship quality, co-residence, repartnering, and having additional biological or stepchildren highlight the importance of (step)parents' willingness to interact with each other, structural opportunities for parent-child interactions, and parents' shifting loyalties from their ex-partner to their new family. ; Fragestellung: Wir untersuchen, ob getrennte/geschiedene Eltern die Geburtstage ihrer biologischen Kinder mit ihren Ex-Partner*innen und ihren neuen Partner*innen feiern, und ob sie den Geburtstag zusammen zu dritt feiern. Hintergrund: Familienrituale wie Geburtstagsfeiern ...