The interaction between dendritic cells and T cells is crucial for the regulation of immunological tolerance and immunity. Although our understanding of the mechanisms responsible for these phenomena has advanced significantly in recent years, we are still lacking a fully integrated model of how dendritic cell phenotype correlates with function, and how complex interactions with multiple dendritic and T cell subpopulations shape the course of the immune response in vivo. In this review, we summarize the current state of knowledge in the field, highlighting the areas where further investigation is likely to advance our understanding of this fundamental immunological interaction.