  Linear Complementary Dual codes (LCD) are binary linear codes that meet their
dual trivially. We construct LCD codes using orthogonal matrices, self-dual
codes, combinatorial designs and Gray map from codes over the family of rings
$R_k$. We give a linear programming bound on the largest size of an LCD code of
given length and minimum distance. We make a table of lower bounds for this
combinatorial function for modest values of the parameters.
