Based on the Job Demands-Resources (JDR) model (E. Demerouti, A. B. Bakker, F. Nachreiner, & W. B. Schaufeli, 2001, The job demands-resources model of burnout. Journal of Applied Psychology, 86, 499-512) and Conservation of Resources (COR) theory (S. E. Hobfoll, 2002, Social and psychological resources and adaptation. Review of General Psychology, 6, 307-324), we tested three competing models that predict different directions of causation for relationships over time between family-supportive work environments (FSWE) and psychological strain, with two waves of data from a military sample. Results revealed support for both the JDR and COR theories, first in the static model where FSWE at Time 1 predicted psychological strain at Time 2 and when testing the opposite direction, where psychological strain at Time 1 predicted FSWE at Time 2. For change models, FSWE predicted changes in psychological strain across time, although the reverse causation model was not supported (psychological strain at Time 1 did not predict changes in FSWE). Also, changes in FSWE across time predicted psychological strain at Time 2, whereas changes in psychological strain did not predict FSWE at Time 2. Theoretically, these results are important for the work-family interface in that they demonstrate the application of a systems approach to studying work and family interactions, as support was obtained for both the JDR model with perceptions of FSWE predicting psychological strain (in both the static and change models), and for COR theory where psychological strain predicts FSWE across time.