Scholars have not fully theorized the multifaceted, interdependent dimensions within the work-family ‘black box’. Taking an ecology of the life course approach, we theorize common work-family and adequacy constructs as capturing different components of employees' cognitive appraisals of fit between their demands and resources at the interface between home and work. Employees' appraisals of their work-family linkages and of their relative resource adequacy are not made independently but, rather, co-occur as identifiable constellations of fit. The life course approach hypothesizes that shifts in objective demands/resources at work and at home over the life course result in employees experiencing cycles of control, that is, corresponding shifts in their cognitive assessments of fit. We further theorize patterned appraisals of fit are key mediators between objective work-family conditions and employees' health, well-being and strategic adaptations. As a case example, we examine whether employees' assessments on 10 dimensions cluster together as patterned fit constellations, using data from a middle-class sample of 753 employees working at Best Buy's corporate headquarters. We find no single linear construct of fit that captures the complexity within the work-family black box. Instead, respondents experience six distinctive constellations of fit: one optimal; two poor; and three moderate fit constellations.