Normative references for POSIX.1-2008 are defined in the Base Definitions volume of POSIX.1-2008.
The following documents are referenced in POSIX.1-2008:
Part 1: Latin Alphabet No. 1
Part 2: Latin Alphabet No. 2
Part 3: Latin Alphabet No. 3
Part 4: Latin Alphabet No. 4
Part 5: Latin/Cyrillic Alphabet
Part 6: Latin/Arabic Alphabet
Part 7: Latin/Greek Alphabet
Part 8: Latin/Hebrew Alphabet
Part 9: Latin Alphabet No. 5
Part 10: Latin Alphabet No. 6
Part 11: Latin/Thai Alphabet
Part 13: Latin Alphabet No. 7
Part 14: Latin Alphabet No. 8 (Celtic)
Part 15: Latin Alphabet No. 9
Part 16: Latin Alphabet No. 10
Volume 1: XVS Commands and Utilities (ISBN: 0-444-70174-5)
Volume 2: XVS System Calls and Libraries (ISBN: 0-444-70175-3)
Commands and Utilities, Issue 3 (ISBN: 1-872630-36-7, C211); this specification was formerly X/Open Portability Guide, Issue 3, Volume 1, January 1989, XSI Commands and Utilities (ISBN: 0-13-685835-X, XO/XPG/89/002)
System Interfaces and Headers, Issue 3 (ISBN: 1-872630-37-5, C212); this specification was formerly X/Open Portability Guide, Issue 3, Volume 2, January 1989, XSI System Interface and Headers (ISBN: 0-13-685843-0, XO/XPG/89/003)
Curses Interface, Issue 3, contained in Supplementary Definitions, Issue 3 (ISBN: 1-872630-38-3, C213), Chapters 9 to 14 inclusive; this specification was formerly X/Open Portability Guide, Issue 3, Volume 3, January 1989, XSI Supplementary Definitions (ISBN: 0-13-685850-3, XO/XPG/89/004)
Headers Interface, Issue 3, contained in Supplementary Definitions, Issue 3 (ISBN: 1-872630-38-3, C213), Chapter 19, Cpio and Tar Headers; this specification was formerly X/Open Portability Guide Issue 3, Volume 3, January 1989, XSI Supplementary Definitions (ISBN: 0-13-685850-3, XO/XPG/89/004)
System Interface Definitions (XBD), Issue 4 (ISBN: 1-872630-46-4, C204)
Commands and Utilities (XCU), Issue 4 (ISBN: 1-872630-48-0, C203)
System Interfaces and Headers (XSH), Issue 4 (ISBN: 1-872630-47-2, C202)
System Interface Definitions (XBD), Issue 4, Version 2 (ISBN: 1-85912-036-9, C434)
Commands and Utilities (XCU), Issue 4, Version 2 (ISBN: 1-85912-034-2, C436)
System Interfaces and Headers (XSH), Issue 4, Version 2 (ISBN: 1-85912-037-7, C435)
System Interface Definitions (XBD), Issue 5 (ISBN: 1-85912-186-1, C605)
Commands and Utilities (XCU), Issue 5 (ISBN: 1-85912-191-8, C604)
System Interfaces and Headers (XSH), Issue 5 (ISBN: 1-85912-181-0, C606)
Base Definitions (XBD), Issue 6 (ISBN: 1-931624-43-7, C046)
System Interfaces (XSH), Issue 6 (ISBN: 1-931624-44-5, C047)
Shell and Utilities (XCU), Issue 6 (ISBN: 1-931624-45-3, C048)
Parts of the following documents were used to create the base documents for POSIX.1-2008:
UNIX System V Release 2.0 Programmer's Reference Manual (April 1984 - Issue 2).
UNIX System V Release 2.0 Programming Guide (April 1984 - Issue 2).