This book constitutes the refereed proceedings of the 11th International Workshop on Cooperative Information Agents, CIA 2007, held in Delft, The Netherlands, September 19-21, 2007.

The 19 revised full papers presented together with 4 invited papers were carefully reviewed and selected from 38 submissions. The papers are organized in topical sections on Information Search and Processing, Applications, Rational Cooperation, Interaction and Cooperation and Trust.

We have described the development of a new micro-payment system, NetPay, f- turing different ways of managing electronic money, or e-coins. NetPay provides an off-line, anonymous protocol that supports high-volume, low-cost electronic trans- tions over the Internet. We developed three kinds of e-wallets to manage coins in a NetPay-based system: a sever-side e-wallet allowing multiple computer access to- coins; a client-side e-wallet allowing customer PC management of the e-coins, and a cookie-based e-wallet cache to improve performance of the client-side e-wallet c- munication overhead. Experiences to date with NetPay prototypes have demonstrated it provides an effective micro-payment strategy and customers welcome the ability to manage their electronic coins in different ways. References 1. Dai, X. and Lo, B.: NetPay - An Efficient Protocol for Micropayments on the WWW. Fifth Australian World Wide Web Conference, Australia (1999) 2. Dai, X., Grundy, J. and Lo, B.: Comparing and contrasting micro-payment models for- commerce systems, International Conferences of Info-tech and Info-net (ICII), China (2001) 3. Dai, X., Grundy, J.: Architecture of a Micro-Payment System for Thin-Client Web App- cations. In Proceedings of the 2002 International Conference on Internet Computing, Las Vegas, CSREA Press, June 24-27, 444--450 4. Dai, X. and Grundy J.: "Customer Perception of a Thin-client Micro-payment System Issues and Experiences," Journal of End User Computing, 15(4), pp 62-77, (2003).