1. Introduction  
2. Observations and spectral data  
3. $\mathtt{C}_{2}$ models and measurements  
4. $\tt{C}_{3}$ models and measurements  
5. $\mathtt{C}_{2}$ versus $\tt{C}_{3}$  
6. $\mathtt{C}_{2}$, DIBs, and $\mathtt{C}_{2}$ DIBs  
7. One step further: Search for more complicated carbon chains  
8. Summary