The 8th International Workshop on Human Leucocyte Differentiation Antigens (chaired by HZ and managed by BS)was run over a 4-year period and culminated in a conference in December 2004. Here we review the achievements of the HLDA Workshops and provide links to information on CD molecules and antibodies against them, including the 93new CDs assigned in the 8th Workshop. We consider what remains to be achieved (including an estimate of the number of leucocyte surface molecules still to be discovered), and how the field can best move forward.