Perceptions of work-to-family conflict reflect incompatible demands and insufficient resources of work and family roles, so that participation in the family role is more difficult because of participation in the work role (Voydanoff, 2005). Studying work-to-family conflict is important because it has been related to outcomes in the work (e.g. turnover intentions, performance, job satisfaction) and family sphere (e.g. life and marital satisfaction, health). However, most research in this domain is cross-sectional, so it is difficult to draw conclusions about causality. Therefore we studied work-to-family conflict in a longitudinal study spanning seven years. Further, we studied work-to-family conflict in couples because previous research and theorizing suggests that work-to-family conflict is the result of a dynamic process that unfolds within the couple. In the present study, we used data from the Swiss Household Panel (SHP), i.e., a yearly panel study which follows a random sample of households in Switzerland. More specifically, we analyzed perceived work-to-family conflict and indicators of changes in role demands and resources in a subsample of 705 couples, over seven measurement points. Results illustrate how perceived work-to-family conflict co-evolves in couples over time. Moreover, they demonstrate how changes in role demands (e.g. work: paid work hours; family: household demands) and/or resources (e.g. work: autonomy; family: spouse support) affect perceived conflict, thus providing important insights about the causes of work-to-family conflict. As such, results have important implications for designing effective organizational policies intended to improve work-family balance.