Objectives: The aim of this two-wave study has been to test the spillover and crossover of job and family demands on changes in perceived stress at work and in the family. Specifically, we proposed that demands from one domain (work or family) spilled over to another domain through interrrole conflict (work–family/family–work conflict) and context-specific self-efficacy. Additionally, we hypothesized that changes in perceived stress were impacted not only by a person’s own demands through interrole conflict but also by the demands of one’s significant other, in the process of crossover. Material and Methods: The study was of dyadic design and it was conducted online, among 130 heterosexual couples, at 2 time points separated by 3 months interval. Hypotheses were verified by means of the path analysis. Results: No support was found for the spillover of job and family demands on changes in perceived stress through interrole conflict and self-efficacy, neither for women nor for men. With regard to the crossover, no support was found for the actor effects, i.e., a person’s demands did not impact changes in one’s own work- and family-related perceived stress but partial support was found for the partner effects, i.e., women’s job demands were associated with men’s changes in work and family-related stress through women’s work–family conflict, and men’s family demands were associated with women’s change in family-related perceived stress through men’s family–work conflict. Conclusions: The study is a longitudinal test of the Spillover–Crossover model and Work–Home Resources model demonstrating that job and family demands are transmitted across domains and across partners in the intimate relationships through the interrole conflict but the nature of this crossover is different for men and women. Int J Occup Med Environ Health 2018;31(2)199–215