Standard Method for Determining the Sound Transmission Class Rating for Masonry Walls (TMS 0302-07) (hereinafter referred to as the Standard) was developed by The Masonry Society's Standards Development Committee. The Standard provides minimum requirements for rating masonry walls for a sound transmission class (STC) based on field or laboratory testing or based on a calculation procedure. Some of the topics covered include reference standards, definitions and notations, materials, construction, quality assurance and sound transmission class rating. The Standard is written as a legal document in mandatory language so that it may form a part of a legally adopted building code. The Commentary presents background details, committee considerations, and research data used to develop the Standard.