This document is an Envelope Reference Guide that provides detailed specifications for various envelope sizes, including commercial, catalog, booklet, announcement, baronial, square, and remittance envelopes. It outlines the dimensions for each envelope type, specifying both envelope and insert sizes. Additionally, the guide explains the anatomy of an envelope, detailing components such as the flap, front, back, and various seam types. It also describes different seal types, including re-moistening seals, split seals, pressure-sensitive seals, self-adhesive seals, clasp seals, and string & button closures. The document further clarifies the differences between catalog and booklet envelopes based on their opening styles. Instructions for measuring envelopes are included, emphasizing the importance of pre-measurement checks and proper measurement techniques. The guide concludes with information on window envelopes, specifying standard window sizes and positioning guidelines, as well as material requirements for window covers.