The official site for PKCS. The standards are available in ASCII, Word, and PostScript formats. (RSA Laboratories)

This document describes a method for encrypting data using the RSA public-key cryptosystem. (B. Kaliski / RSA Laboratories East)

This document describes the PKCS #10 format, a syntax for certification requests. (B. Kaliski / RSA Laboratories East)

This document describes a general syntax for data that may have cryptography applied to it, such as digital signatures and digital envelopes. (B. Kaliski / RSA Laboratories, East)

This document provides recommendations for the implementation of public-key cryptography based on the RSA algorithm. (B. Kaliski, J. Staddon / RSA Laboratories)

PKCS explained. From the RSA labs FAQ.