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Uncertainty is a feeling of doubt or not knowing that permeates the experiences of family caregivers. This paper explores states of uncertainty faced by family caregivers who provide end of life care. First, a series of research projects exploring the concept of uncertainty are summarized in a theory of caregiver uncertainty. Critical to this discussion are the critical conceptual components of the experience of uncertainty: Sensing confidence, Sensing control, Reading the situation, Shifting temporal perspectives, and Building a sense of normal. The interplay of these conceptual components mark states of uncertainty that range in intensity and duration across the caregiving experience. In order to understand the experience of uncertainty within the context of end of life caregiving, grounded theory study methods were used to explore variations in states of uncertainty experienced by caregivers who provided end of life care. The sample consisted of 48 family caregivers of adult patients with varied death trajectories: cancer, organ failure, ALS, and frailty. The caregiving experience was punctuated by three crisp transitions: diagnosis, recognition of the ineffectiveness of curative treatment, and the death of the loved one. Surrounding each of these transition points, the caregivers lived through phases described as: Something's not right, Challenging normal, Building a new normal, and Grieving the loss while building a new life. Changing patterns of the essential characteristics of uncertainty marks each of these phases.