Two forms of relations-dependence and interdependence-are the basis fo
r two distinct types of social structure: 1) exchange relations and ne
tworks, and 2) groups. The structure of mutual dependence that underli
es all social exchange relations is riskier than the structure of inte
rdependence that underlies cooperation in groups. I argue that the ris
k of dependence is reduced, to varying degrees, by the way in which tr
ansactions are structured and organized over time. I discuss: 1) the f
orm of transactions (negotiated or reciprocal) and 2) the relations be
tween sequential transactions (independent or serially-dependent). Bot
h negotiated transactions and serially dependent transactions reduce r
isk, in different ways and to varying degrees. The joint decision proc
ess of negotiated transactions changes the structure of exchange direc
tly, by introducing elements of interdependence. Serially dependent tr
ansactions provide actors with the opportunity to change the structure
, through the use of contingent action, and allow for the development
of emergent aspects of exchange. Implications for research are discuss
ed.