NGST and the Physical Exploration of Galaxy Evolution During the Era   2<z<5
  NGST offers unprecedented opportunities for charting the `dark ages' beyond the limits of the deep optical surveys conducted with HST. An equally important motivation, however, is a detailed physical understanding of the later stages of cosmic history including the period 2<z<5 when most galaxies are thought to assemble and undergo dramatic changes in their star formation rate, chemical content and, ultimately, their morphological characteristics. An important question we need to resolve is the extent to which established massive systems might exist at moderate redshifts. In the context of recent observational and theoretical progress in this area, I review the role NGST could play in this redshift range taking into account the likely progress made in the next decade with the new generation of 8-m class ground-based telescopes 
Richard S Ellis (IoA, Cambridge)