The theory of joint and several liability (“solidary obligations” in the Continental legal systems) is conceived as a way of protecting a creditor’s interests. Accordingly, its distinctive feature consists of the so-called libera electio (“free choice”) held by the creditor. Where two or more debtors are jointly and severally liable for the same performance, the creditor will always be entitled to claim it from any one of them. Thus, in the ordinary case, the creditor will presumably opt for the wealthiest among the co-debtors. This is a well-established mechanism stretching back to the Roman legal tradition. It is today widely encountered in national civil codes and also acknowledged by the common law. In particular, the broad powers historically granted to the creditor stem from a specific view of joint and several liability, one which was passed down from Roman Law and, despite some uncertainties, through the ius commune. However, from a comparative law perspective, some doubts about such an entrenched conception are raised by cases in which it applies to co-debtors who are obliged in respect of arguably diverging interests—with instances of suretyship being a particularly good example. This circumstance leads one to reflect upon the nature of joint and several liability in an attempt to ascertain whether the libera electio is always an essential element of this kind of liability. In this respect, special attention should be paid when one of the co-debtors is in a weak position. On the whole, the juridical nature of joint and several liability brings about a new configuration of the legal relationship between a creditor and her co-debtors (and between co-creditors and a debtor). In this chapter a general principle is elaborated: if a joint and several (co-)obligor is responsible only for a debt owed by another, the creditor must first seek payment from the co-debtor in the interest of whom the debt group is bound. This need to rank the claims towards primary and secondary debtors does not result in the widespread “benefit of discussion”, which entails a procedure of attempting judicial execution against the main debtor before suing the subsidiary debtor. On the contrary, the creditor must primarily pursue her legal interests outside of court. Only once it is clear that the primary debtor is not able to pay may the creditor approach the other co-debtor(s).