The effects of cyano substitution on cyclobutadiene are explored using density functional. coupled-cluster, CASSCF, and CASPT2 calculations. An isodesmic reaction is employed to gauge the relative stabilization (Delta H-xn degrees) of cyclobutadienes with varying numbers of cyano groups. Although density functional theory predicts a relatively large stabilization for the addition of four cyano substituents to cyclobutadiene (18.5 kcal/mol), coupled-cluster theory predicts a smaller stabilization (9.3 kcal/mol). The effect of the number of cyano groups on the singlet triplet gaps is also investigated. NBO calculations lend insight into the structural trends of the triplets, and the comparison of coupled-cluster and CASSCF calculations sheds light on the multi reference electronic character in these systems. The effect of tetracyano substitution on tetrahedrane and other C4H4 isomers is also explored.