  We analyze various brane configurations corresponding to field theories in
three, four and five dimensions. We find brane configurations which correspond
to three dimensional N=2 and four dimensional N=1 supersymmetric QCD theories
with quartic superpotentials, in which what appear to be ``hidden parameters''
play an important role. We discuss the construction of five dimensional N=1
supersymmetric gauge theories and superconformal fixed points using branes,
which leads to new five dimensional N=1 superconformal field theories. The same
five dimensional theories are also used, in a surprising way, to describe new
superconformal fixed points of three dimensional N=2 supersymmetric theories,
which have both ``electric'' and ``magnetic'' Coulomb branches.
