  We study the low energy behaviour of N=(2,2) supersymmetric gauge theories in
1+1 dimensions, with orthogonal and symplectic gauge groups and matters in the
fundamental representation. We observe supersymmetry breaking in
super-Yang-Mills theory and in theories with small numbers of flavors. For
larger numbers of flavors, we discover duality between regular theories with
different gauge groups and matter contents, where regularity refers to absence
of quantum Coulomb branch. The result is applied to study families of
superconformal field theories that can be used for superstring
compactifications, with corners corresponding to three-dimensional Calabi-Yau
manifolds. This work is motivated by recent development in mathematics
concerning equivalences of derived categories.
