Expectations about stand-alone and network benefits determine the adoption decision of cus- tomers and hence the diffusion of standards. To increase the number of adopters of a communi- cation standard like EDI, not only the ability to exchange messages (as a source of direct net- work effects), but also the provision of comple- mentary services such as standardized master data, e.g., by establishing a central, industry- wide EDI data pool (as a source of indirect net- work effects) is important. We thus examine the differing impact of direct and indirect network effects on the adoption and diffusion of commu- nication standards. The incorporation of both network benefits into an agent-based simulation model may help to better understand the under- lying diffusion problem.