With regard to local development, I discuss a cluster of situations which could promote cooperation due to a lack of previous trust. These situations derive from a set of multiple "network effects" depending on a context in which the expected benefit deriving from a good or a service depends on the number of actors using this good or service. I will first focus on network effects on markets with technological innovations and product innovations and then deal with network effects that can be observed in traditional markets and in non-market environments. I will argue that network effects contribute to the creation of inter-individual transaction spaces with a local maximum of cohesion which may facilitate collective processes of learning through negotiation. Neither does trust play the role of an essential prerequisite in these processes nor does people negotiate in an experimental way as nobody knows adequately the advantages and costs of one's own position in the network of the effects of networks. This kind of interpretation is supposed to show some potentialities of one of the most innovative and powerful instruments of endogenous promotion of local development, namely the territorial agreements.