The present document provides guidance on the use of standards for Trust Application Service Providers (area 5) as identified in the framework for standardization of signatures: overview [i.1]. The present document then describes the Business Scoping Parameters relevant to this area (see clause 6) and how the relevant standards and options for this area can be identified given the Business Scoping Parameters (clause 7). The target audience of the present document includes: 1) Business managers who potentially require support from digital signatures in their business will find here an understandable explanation of how services applying digital signatures standards can be used to meet their business needs. 2) Application architects who will find here material that will guide them throughout the difficult process of designing a system that fully and properly satisfies all the business and legal egulatory requirements specific to services applying digital signatures@ and will gain a better understanding on how to select the appropriate standards to be implemented and/or used. 3) Developers of the systems who will find an understanding of a good part of the ultimate reasons that led the systems to be designed as they were@ as well as a proper knowledge of the standards that exist in the field and to be known in detail for a proper development.