This study explored informal family caregiver experiences in supporting care transitions between hospital and home for medically complex older adults. Using a qualitative, grounded-theory approach, in-depth semi-structured interviews were conducted with community and resource case managers, as well as with informal caregivers of older hip-fracture and stroke patients, and of those recovering from hip replacement surgery. Six properties characterizing caregiver needs in successfully transitioning care between hospital and home were integrated into a theory addressing both a transitional care timeline and the emotional journey. The six properties were (1) assessment of unique family situation; (2) practical information, education, and training; (3) involvement in planning process; (4) agreement between formal and informal caregivers; (5) time to make arrangements in personal life; and (6) emotional readiness. This work will support research and clinical efforts to develop more well-informed and relevant interventions to most appropriately support patients and families during transitional care.