Introduction 2005 2007 2007 2002a 2000a 2007 2002 2004 2005 2006 2005 2001 Unraveling the intrinsic complexity of the endo-lysosomal system is a major challenge for cell biologists. Here, we will review some of the current insights in the mechanisms involved in lysosome biogenesis and functioning. Imaging of the endo-lysosomal system combined with imaginative visions has been instrumental for furthering the conceptual understanding of the endo-lysosomal system. Therefore, on the special occasion of the 50th anniversary of the Journal of Histochemistry and Cell Biology, we will also highlight some examples in the literature showing how imaging, especially electron microscopy (EM), has contributed to our understanding of the endo-lysosomal system today. The discovery of the lysosome 1981 2005 1955 1 1956 1952 1962 1959 1961 1961 2 Fig. 1 arrows MT ER 1956  Fig. 2 1961 LY  BC  ER  EX  MI  V  1954 1956) 1959 The endocytic pathway in a nutshell 3 2003 2005 2007 2003 3 trans 3 3 1996 2007 Fig. 3 a b c AP ER M6P MPR SAP SNX1 TGN trans  Defining early and late endosomes 2007 TGN-to-endosome transport pathways 3 1987 2003 1989 1991 MPR-dependent transport of soluble lysosomal hydrolases 2008 1997 1985a b 2003a 3 1985a b 1981 1988 1984 1985 1988 1993 1998) 4 2000 2000b 2000 2000 2002 2003 2002 2003b Fig. 4  AP-1  TGN arrowheads  CI-MPR  AP-1  TGN G  MPR-independent transport of soluble lysosomal hydrolases 3 1988 1988 1988 2002 1990 1988 1985 1991 2007 3 1981 1981 3 5 1987 1982 1982 2007 1999 Fig. 5 L  D  Bar  M2 M2 2003 1994 2007 2005 TGN-to-lysosome transport of lysosomal membrane proteins 1992 2005 2003 2003 1996 1996 2000 2005 1998 2005 3 1997 1996 1999 2003 1996 2006 The early endosome: from CURL to tubular sorting endosome 3 1983 6 Fig. 6  Left panel 1983  Right panel 2004  LAMP-1  3 3 2007 6 1999 1998 2004 3 2004 2004 2002 2005 2004 2000 1998 2002 3 6 2004 2006 3 Multiple sorting events at the early endosomal limiting membrane 3 2007 2004 2005 2007 2004 3 2006 2004 2002 2001 2002b Sorting to late endosomes and lysosomes  1988 1984 2004 2002 2002b 2002b 2003 2003 2003b 2001 2002 2003 2002b 2002b 2006 2005 2003a 2003 2004 2004 2003 Future developments 2006 2006 2003 2006 2003 7 2006 2007 Fig. 7 LE  D  G Bar  2002 2003 2004 2006 2004 2007 Finally, with the development of live cell imaging methods and correlative live cell imaging EM, a unique tool is provided to integrate dynamic parameters with ultrastructural protein localization studies, which opens a whole new field of analysis.