| 1321 | The MD5 Message-Digest AlgorithmR. Rivest | Informational | April 1992 |
| 1851 | The ESP Triple DES TransformP. Karn, P. Metzger, W. Simpson | Experimental | September 1995 |
| 2119 | Key words for use in RFCs to Indicate Requirement LevelsS. Bradner | Best Current Practice | March 1997 |
| 3174 | US Secure Hash Algorithm 1 (SHA1)D. Eastlake 3rd, P. Jones | Informational | September 2001 |
| 3261 | SIP: Session Initiation ProtocolJ. Rosenberg, H. Schulzrinne, G. Camarillo, A. Johnston, J. Peterson, R. Sparks, M. Handley, E. Schooler | Proposed Standard | July 2002 |
| 3435 | Media Gateway Control Protocol (MGCP) Version 1.0F. Andreasen, B. Foster | Informational | January 2003 |
| 3447 | Public-Key Cryptography Standards (PKCS) #1: RSA Cryptography Specifications Version 2.1J. Jonsson, B. Kaliski · obsoleted by RFC 8017 | Informational | February 2003 |
| 3454 | Preparation of Internationalized Strings ("stringprep")P. Hoffman, M. Blanchet · obsoleted by RFC 7564 | Proposed Standard | January 2003 |
| 3491 | Nameprep: A Stringprep Profile for Internationalized Domain Names (IDN)P. Hoffman, M. Blanchet · obsoleted by RFC 5891 | Proposed Standard | March 2003 |
| 3525 | Gateway Control Protocol Version 1C. Groves, Ed., M. Pantaleo, Ed., T. Anderson, Ed., T. Taylor, Ed. · obsoleted by RFC 5125 | Historic | June 2003 |
| 3550 | RTP: A Transport Protocol for Real-Time ApplicationsH. Schulzrinne, S. Casner, R. Frederick, V. Jacobson | Internet Standard | July 2003 |
| 3629 | UTF-8, a transformation format of ISO 10646F. Yergeau | Internet Standard | November 2003 |
| 3761 | The E.164 to Uniform Resource Identifiers (URI) Dynamic Delegation Discovery System (DDDS) Application (ENUM)P. Faltstrom, M. Mealling · obsoleted by RFC 6116, RFC 6117 | Proposed Standard | April 2004 |
| 3932 | The IESG and RFC Editor Documents: ProceduresH. Alvestrand · obsoleted by RFC 5742 | Best Current Practice | October 2004 |
| 3986 | Uniform Resource Identifier (URI): Generic SyntaxT. Berners-Lee, R. Fielding, L. Masinter | Internet Standard | January 2005 |
| 4301 | Security Architecture for the Internet ProtocolS. Kent, K. Seo | Proposed Standard | December 2005 |
| 4347 | Datagram Transport Layer SecurityE. Rescorla, N. Modadugu · obsoleted by RFC 6347 | Historic | April 2006 |
| 4395 | Guidelines and Registration Procedures for New URI SchemesT. Hansen, T. Hardie, L. Masinter · obsoleted by RFC 7595 | Best Current Practice | February 2006 |
| 4566 | SDP: Session Description ProtocolM. Handley, V. Jacobson, C. Perkins · obsoleted by RFC 8866 | Proposed Standard | July 2006 |
| 4647 | Matching of Language TagsA. Phillips, Ed., M. Davis, Ed. | Best Current Practice | September 2006 |
| 4733 | RTP Payload for DTMF Digits, Telephony Tones, and Telephony SignalsH. Schulzrinne, T. Taylor | Proposed Standard | December 2006 |
| 4734 | Definition of Events for Modem, Fax, and Text Telephony SignalsH. Schulzrinne, T. Taylor | Proposed Standard | December 2006 |
| 5125 | Reclassification of RFC 3525 to HistoricT. Taylor | Informational | February 2008 |
| 5234 | Augmented BNF for Syntax Specifications: ABNFD. Crocker, Ed., P. Overell | Internet Standard | January 2008 |
| 5457 | IANA Considerations for IAX: Inter-Asterisk eXchange Version 2E. Guy, Ed. | Informational | February 2010 |
| 5646 | Tags for Identifying LanguagesA. Phillips, Ed., M. Davis, Ed. | Best Current Practice | September 2009 |
| 5741 | RFC Streams, Headers, and BoilerplatesL. Daigle, Ed., O. Kolkman, Ed., IAB · obsoleted by RFC 7841 | Informational | December 2009 |