  The most general linear and local set of boundary conditions, involving
relations between the normal components of the D and B vectors and tangential
components of the E and H vectors at each point of the boundary, are considered
in this paper. Reflection of a plane wave from a boundary defined by general
conditions in an isotropic half space is analyzed and an analytic expression
for the reflection dyadic is derived. It is shown that any plane wave can be
decomposed in two components which do not interact in reflection. Properties of
plane waves matched to the general boundary are given. Certain special cases of
boundary conditions, arising naturally from the general theory and labeled as
E-boundary, H-boundary and EH-boundary conditions, are introduced as
interesting novelties and some of their properties are studied. Previously
known special cases are considered in verifying the theory. A possible
realization of the general boundary in terms of an interface of a general
bi-anisotropic medium is discussed in an Appendix.
