The FHIR Implementation Guide for the Human Services Data Specification (HSDS) will describe the architectural considerations for accessing data from a directory of social services. The Guide will specify methods of aligning FHIR resources – specifically, those that describe healthcare provider directory information – with HSDS, an industry standard for service directory data exchange that describes information about human service agencies, the services they provide, and the locations where they are offered.  The Guide will also specify RESTful methods of for accessing data from HSDS-compliant directories, in alignment with the Human Service Data API protocols (HSDA). Each profile within will define the minimum mandatory elements, extensions and terminology requirements that MUST be present to enable interoperability between FHIR systems and sources of HSDS data. This project will be conducted in collaboration with the leadership of the Open Referral Initiative, which will develop a FHIR-specific profile of HSDS for use in conjunction with the FHIR HSDS IG; Open Referral will also develop an upgrade to HSDA, the standardized API protocols, to establish alignment with the FHIR profile. This project will engage with the Administration of Community Living and the participants in ACL's Social Care Referrals challenge as key stakeholders and prospective implementation partners. Because our effort leverages the Human Services Data Specification (HSDS) https://docs.openreferral.org/en/latest/hsds/ as our data model and its suite of APIs as the basis for use cases and behavior. It was suggested the project includes development of a domain analysis model (DAM) reflecting our analysis upon which to base new profiles for the FHIR IG for the Human Service Resource and Provider Directories (This IG reflects constraints on the existing PDEX Plan-Net Provider Directory IG STU1, is and intended to be published a "companion guide" to the PDEX provider directory). In addition, this FHIR implementation guide will use the US Core profiles. If this FHIR implementation guide is unable to use a US Core profile, we will follow the Cross Group Projects WG's variance request process, and provide the US Realm Steering Committee an approved rationale for deviation in the implementation guide where applicable.