The four-volume SP 800-63 Digital Identity Guidelines document suite is available in both PDF format and online.

PDF versions of the documents are available from:

Document Title URL SP 800-63-3 Digital Identity Guidelines https://doi.org/10.6028/NIST.SP.800-63-3 SP 800-63A Enrollment and Identity Proofing https://doi.org/10.6028/NIST.SP.800-63a SP 800-63B Authentication and Lifecycle Management https://doi.org/10.6028/NIST.SP.800-63b SP 800-63C Federation and Assertions https://doi.org/10.6028/NIST.SP.800-63c

Links to the online version of the SP 800-63 suite are below.

Additional informative resources: