Communication about prognosis is integral to effective palliative care. However, prognosis communication often entails considering mortality, which can trigger existential questions. We understand very little about how existential experience is communicated in palliative care conversations. To fill this gap, this dissertation addresses the following aims: (1) Clarify the concept of the existential experience within the context of adults with advanced cancer (Chapter 2); (2) Describe how patients, families, and clinicians communicate about existential experience in palliative care conversations (Chapter 3); and (3) Explore the intersection between prognosis communication and existential dimensions of conversation (Chapter 4). To accomplish Aim 1, we synthesized published qualitative literature regarding how adults with advanced cancer describe their existential experience. Using Rodgers’ evolutionary method of concept analysis, we conceptualize existential experience as a dynamic state, preceded by confronting mortality, defined by diverse reactions to shared existential challenges related to parameters of existence (body, time, others, and death), resulting in a dialectical movement between existential suffering and joy. To address Aims 2 and 3, we analyzed a randomly selected subset of an existing Palliative Care Communication Research Initiative (PCCRI) study dataset. PCCRI data includes verbatim transcripts of inpatient palliative care consultations with adults with advanced cancer. Using a qualitative descriptive approach, we found that overall, existential communication was woven within palliative care conversations, and related to key themes of: 1) Time as a pressing boundary; 2) Maintaining a coherent self; and 3) Connecting with others. In Chapter 4, we took a mixed methods approach, quantitatively stratifying the study sample by levels of prognosis communication and qualitatively describing existential dimensions of conversations within and across none, low, and high levels of prognosis communication. We found existential and prognosis communication were deeply interconnected. Additionally, existential communication was more common within conversations with higher levels of prognosis communication, representing an existential shift compared to the more physical focus of conversations with no prognosis communication. This dissertation generates new knowledge about how existential experience is communicated during naturally-occurring palliative care conversations. Our findings have implications for improving how we communicate with, and care for, individuals with advanced cancer and their families.