Background: It is unclear when people with amyotrophic lateral sclerosis and their family carers think about their future, what they would prefer in terms of care, and how their ideas change over time. Aim: Understanding experiences with advance care planning of persons with amyotrophic lateral sclerosis and their family carers—and if, when, how, and why these experiences change over time. Design: A qualitative longitudinal interview study. Analysis involved content analysis, followed by a two-step timeline method to describe changes in advance care planning experiences within and across participants. Setting/participants: Nine persons with amyotrophic lateral sclerosis and nine family carers who were interviewed three times over a 9-month period. Results: All participants thought about future care, but few talked about it. Over time, advance care planning experiences were influenced by intertwined elements: (1) experienced physical decline and related future care needs; (2) how persons with amyotrophic lateral sclerosis identify themselves as patients; (3) obtaining information about diagnosis and prognosis; (4) professionals initiating conversations about medical aspects of end-of-life decisions; (5) balancing between hope to remain stable and worry about the future; and (6) protecting themselves and each other from worries about the future. Conclusion: This study emphasizes how factors such as coping with the disease and relational dynamics shape individuals’ thoughts about future care over time and how psychological, social, and medical factors are interwoven in advance care planning. The findings advocate for a process-oriented perspective, portraying advance care planning as an ongoing dialog, encompassing the needs, concerns, and emotions of both people with amyotrophic lateral sclerosis and their family carers.