We present recent results on the properties of ordered group IV compounds containing carbon, silicon and germanium. Our calculations are done using a full-potential -linearized muffin-tin orbital (FP-LMTO) method within the local density approximation (LDA). Twenty-seven fully relaxed compounds represented by six different compound structures have been examined. With the exception of SiC, all compounds are found to be metastable. Two trends emerge: compounds that have carbon on a common sublattice are less unbound because of their relatively low strain, and carbon-germanium bonds are disfavored. Simple two-body (bond-length) and three-body (bond-angle) empirical fits to our first-principles results are not adequate to predict excess energies with sufficient accuracy to be reliably predictive for other structures. Some compounds have direct gaps. When carbon shares a sublattice with silicon or germanium, the large strain results in a narrowing of the band gap, and in some cases the compound is metallic. The most promising structures with the lowest excess energy contain carbon on one sublattice and do not lattice match to silicon, but match rather well to silicon carbide.