Many of the physical requirements for concrete masonry units (CMU) contained in ASTM C90, Standard Specification for Concrete Masonry Units, had remained unchanged for many years. The requirements for web thickness, for example, were introduced in the 1950s, representing the best practices for production at that time. These requirements remained essentially unchanged until 2011 when significant changes were incorporated. With a changing environment for building requirements, especially those related to energy efficiency and sustainability, the need for the concrete masonry unit to evolve has become evident. In late 2011, the minimum web requirements in ASTM C90 were significantly revised to provide new flexibility in CMU unit design/configuration. These changes, based on a rational review of the factors that affect minimum web thickness, provide CMU producers, specifiers, and contractors with means to adjust unit configurations to meet the needs of their market. Additionally, as a result of research performed by the National Concrete Masonry Association on CMU prism strengths, the minimum compressive strength required by ASTM C90 was increased from 1900 psi (13.1 MPa) to 2000 psi (13.8 MPa). This change, coupled with revisions to the unit strength method for determining compliance with the specified compressive strength of masonry [see TMS 602/ACI 530.1/ASCE 6, 2011, “Specification for Masonry Structures,” Masonry Standards Joint Committee, Longmont, CO] can provide more economical designs and cost-competitive construction. These changes are significant revisions to this specification, and the potential impact to the industry is large. This paper reviews these changes to ASTM C90, the rationale supporting the changes, and the impacts to the concrete masonry industry and concrete masonry construction.