This paper examines the import and nature of the autonomy principle as applied to documentary letters of credit and other payment instruments. It argues that, while autonomy appears to have developed a degree of normativity, it is not a mandatory principle, but rather one that is subject in some degree to party autonomy. It follows that parties are free to choose whether they wish the doctrine of autonomy or only certain aspects to govern their dealings, but this is likely to have an impact upon the nature of the resulting instrument. This discussion regarding the nature of the autonomy principle raises the question of whether performance bonds should in principle continue to be treated as autonomous instruments, whether (as suggested academically) they should be placed on a lower point on a supposed scale of autonomy, or whether they are more logically equated with other non-autonomous forms of security. Somewhat controversially, this paper advocates the third of these options.