A uniform, systematic, and complete review is given on s-p hybrid orbitals with which a central atom Z enters into σ bonds with two to four ligands L. All possible cases of symmetry are treated: in four-coordination from Td symmetry in ZL4 molecules to the asymmetric case of four different ligands; in three-coordination from D3h symmetry in ZL3 molecules to Cs symmetry for ZLL′L″ molecules. For some cases the formulas are given for the first time. In this connection it is shown that the most general sp3 and sp2 hybrids still contain three and two free parameters, respectively. The appearance of hybrid orbitals on changing from a “delocalized” to a “localized” description of the bonding situation is illustrated with examples. Finally, possible applications in the description of the bonding relationships of molecules and the interpretation of the results of spectroscopic methods for the determination of molecular structure are indicated and likewise illustrated by examples.