  In this paper, we construct defects (domain walls) that connect different
phases of two-dimensional gauged linear sigma models (GLSMs), as well as
defects that embed those phases into the GLSMs. Via their action on boundary
conditions these defects give rise to functors between the D-brane categories,
which respectively describe the transport of D-branes between different phases,
and embed the D-brane categories of the phases into the category of D-branes of
the GLSMs.
