A survey of some more recent results on the structural chemistry of compounds between transition elements and IVb group elements (carbon, silicon, germanium and tin) will be presented. There are essentially two large classes of compounds to be discussed, characterized by uniform structural principles, namely transition element carbides and related phases on the one hand and defect disilicide structure compounds and derivatives on the other. Starting with the problem of carbon ordering in transition element carbides and hydrogen containing carbides which reveal the significance of the octahedral [ T 6 C ]-group, numerous complex carbides of the general formula T x M y C z (T = transition element, M = another transition or B-group element) can be explained by means of a few common structural features. Perovskite carbides of formula T 3 MC, corresponding to the filled up Cu 3 Au-type or the filled up U 3 Si-type structures, β-Mn carbides of formula T 3 M 2 C, corresponding to the filled up β-Mn-type structure and K-carbides, related to the Mn 3 Al 9 Si-type structure are characterized by linking of the [T 6 C]-groups by corners. H-phase carbides of formula T 2 MC and carbides having Ti 3 SiC 2 -type structure exhibit linking of the [T 6 C]-groups by edges. A similar mode of linking also occurs for carbides with V 3 AsC-type or the filled Re 3 B-type structures, although in some cases such as VCr 2 C 2 the trigonal prismatic [T 6 C]-group intervenes. Finally, the η-carbides having filled Ti 2 Ni-type and carbides of formula T 5 M 3 C with filled up Mn 5 Si 3 -type structure can be regarded as built up by linking of the octahedral [T 6 C]-groups by faces. The geometrical factor within the carbides is strongly supported by the short T-C-distances in the structural element [T 6 C], thus the formation and architecture of complex carbides may be understood from a topo-chemical point of view, for example, Ti 2 GeC (H-phase carbide) consists of the sum of TiC (octahedral group) and TiGe (trigonal prism). The second class of compounds, which are derived from the TiSi 2 -type structure, also belong to an uniform geometrical principle; however, some influence of the electronic concentration on the defect of the B-group element (Si,Ge) and the cell parameter will be recognized. The peculiar structural principle can be described by a partial lattice of the transition metal atom corresponding almost perfectly to that of the Ti-atoms of the TiSi 2 -type while the second partial lattice (Si,Ge or Sn) according to the defect of these atoms is expanding in one direction of the generating (110) plane. As a consequence of the mutual interference of T- and B-group element atoms a helicoidal structural element of the respective Si, Ge, etc., atoms results. Thus, the arrangement is characterized by a typical subcell and occasionally by extremely long c -axis. That also means, fairly complex compositions occur such as Mn 11 Si 19 , Mo 13 Ge 23 , V 17 Ge 31 or Rh 39 (Ga 0.5 Ge 0.5 ) 58 . The problem of pseudo-homogenous domains of compounds arise in as far as within fairly small regions of composition a split according to different multiple of subcell will be observed, such as Mn 11 Si 19 (MnSi 1.727 ); Mn 26 Si 45 (MnSi 1.730 ); Mn 15 Si 25 (MnSi 1.733 ) and Mn 27 Si 47 (MnSi 1.741 ). A similar change in the multiple of subcells that means independent phases, takes place by substituting either the transition element by another or by substituting the B-group element by another B-group element such as Cr 37 Ge 59 As 4 which corresponds to the Rh 10 Ga 17 -type while Cr 11 Ge 19 is isotypic with Mn 11 Si 19 . In general, lowering of the overall electron concentration diminishes the defect of the B-group element in the compound.