XeTeX

[Wolfgang Engelmann]

I get this error:

! Fatal Package fontspec Error: The fontspec package requires either 
XeTeX or
(fontspec)                      LuaTeX.
(fontspec)
(fontspec)                      You must change your typesetting engine to,
(fontspec)                      e.g., "xelatex" or "lualatex"instead of
(fontspec)                      "latex" or "pdflatex".
Type <return> to continue.
  ...     l.45 \msg_fatal:nn {fontspec} {cannot-use-pdftex}
?

at what place do I have to change the typesetting engine?
I have done it at the obvious places, but apparently missed one.

Wolfgang