When I was a lad, the adage that “cells are not simply bags full of enzymes” was already popular in biology, and how true it turned out to be. We now know that eukaryotes comprise cellular compartments whose integrity and composition is maintained by specific mechanisms, including the membrane traffic between membrane-bound organelles. So what attracts cell biologists to the challenge of membrane traffic? One reason may be the complexity in composition and spatio-temporal dynamics -- a complexity that manifests itself in the sheer beauty of the physical forms of the trafficking organelles. Another motivation may be the simple question of how complex mixtures of substances can be moved around selectively in membrane-bound vesicles while maintaining the compositional integrity of organelles. Whatever the attraction, it is clear that the full molecular inventory of traffic machinery will be known soon, and we stand now on the threshold of a deeper understanding. It is therefore a good time to look at what has been achieved so far. Interestingly, the focus of membrane trafficking research has come full circle. Initially, discrete organelles with specialized functions were described and then came a mass of molecular information. Now, we are back to the organelles, trying to work out how they are built and how they function in a dynamic way. As in any story of science, the road to discovery has been crucially dependent on clever insights, married with technical developments at both molecular and atomic resolution.

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