CD data between 185 and 230 nm for 228 chiral olefins have been analysed empirically in order to determine the main features of the relationships between molecular structure and chiroptical properties. Most of the compounds examined are cyclohexene or methylene-cyclohexane derivatives: they include many compounds of steroid type. The regular and generally unstrained structures of such compounds are particularly favourable for initial studies on olefins, as they were earlier for carbonyl compounds. Cyclopentene and methylene-cyclopentane analogues are included for comparison, but are not discussed in detail because of their relatively limited number and less-clearly defined conformations. Olefinic compounds are divided into four classes (A–D), according to their substitution patterns when considered as alkylated ethylene derivatives. In the first stage of the analysis, characteristic wavelengths ar recognised for the two (or three) electronic transitions detectable from the CD curves for each class of olefine. Some of the tetrasubstituted-ethylene analogues have optically-active transitions in the regions ca. 220 nm and ca. 202 nm, but one or other of these transitions may be undetectable from CD surveys for some structural types, a feature not appreciated in earlier discussions of olefin CD. In the second stage of the analysis, the CD curves are studied by the usual empirical method of pairwise comparisons, in order to evaluate the contributions (δΔϵ) of structural features to the observed CD at each of the absorption bands. Each of the four substituted-ethylene classes shows its own characteristic behaviour, confirming that no one symmetry rule can be applicable to all chiral olefins. The main conclusions for the lowest-energy CD band (⩾ 200 nm) are: Class A 1,1- Disubstituted ethylenes. Exocyclic methylene compounds for the most part follow a carbonyl-like “Octant Rule”, the main point of difference being a large consignate (“octant”) contribution from a “β”-axial methyl group, which can outweigh effects of carbocyclic rings; Class B Cis-1,2- disubstituted ethylenes. Cyclohexene analogues give a CD band with sign corresponding to a cosignate effect of allylic axial CH bonds; Class C Trisubstituted ethylenes. Compounds of the “1-methylcyclohexene” type follow those of class (B) fairly closely, but “trisubstituted ethylene” fragments of the ethylidenecyclohexane type, including “Δ” 1(19)-octalin “analogues, give strong CD bonds with signs determined by the chirality of the ethylidenecyclohexane unit; an additional feature of “Δ 1(19)-octalin” analogues is a very large dissignate effect accompanying axial alkyl substitution at the allylic carbon atom trans to the olefinic CH bond: alkyl substitution at the other allylic centres has relatively little effect; Class D Tetrasubstituted ethylenes. These compounds generally show rather weak CD curves, but axial-allylic methyl substituents produce dissignate effects. The CD characteristics associated with the second (higher energy) absorption band (< 200 nm) have also been analysed for each class of olefin, but in less detail because of the lower reliability of data. The sign of this CD band is usually the reverse of that at the lowest energy band, although there are exceptions. The other most noteworthy feature is a significant or even large consignate contribution in some cases when allylic quasi-equatorial alkyl substituents are present.