For three decades, our experiments have emphasized adding CD1 ligands from the outside of cells to measure T cell activation, solve CD1-lipid structures and generate tetramers for T cell sorting. Here we present experimental evidence that emphasizes CD1 capture of endogenous self ligands captured inside cells. By eluting lipids from CD1-lipid complexes formed in cells, lipidomics acts as a relatively unbiased and quantitative approach to measure CD1 antigen display. This ‘inside view' offers advantages by emphasizing naturally occurring ligands in cellular pools and physiological CD1 loading systems. Comparative lipidomics shows that many cellular lipids are captured by CD1a, CD1b, CD1c or CD1d at frequencies that are different from their relative concentration in cellular membranes, allowing identification of named lipids that are overcaptured by the human CD1 system for display, especially sphingolipids. Whereas our prior approaches used T cell activation assays to identify lipid antigens, TCR trap assays separate CD1-lipid complexes formed from endogenous self lipids that do or do not bind to TCRs. Based on analysis of TCR trapping with an type I NKT cell receptor, we will show three classes of self headless antigens found in CD1d-TCR complexes. Because TCR trapping relies on binding rather than activation, it has the ability to detect blockers of T cell binding to CD1. Last, tetramers of CD1 proteins loaded with self lipids have identified large populations of human T cells derived from blood and tissues.