This qualitative study explored the applicability and usefulness of a promising advance care planning (ACP) intervention and examined the ACP process. Nine dyads (patients newly diagnosed with advanced lung cancer and a family member) participated in the ACP intervention, with evaluative interviews at 3 and 6 months after the intervention. All interviews were recorded, transcribed verbatim, and analyzed using constant comparison. The process was found not to be one of preparing a substitute decision-maker to speak for oneself and direct health care at a time when one is incapacitated; rather, the families engaged in a deeply relational process where meaning, values, and preferences were negotiated in conversation. ACP is theoretically rooted in a traditional notion of patient autonomy that is not aligned with the relational process that unfolded in this study. An approach that embraces relational autonomy is more congruent and provides a stronger foundation for meeting the needs of families.