The ACER critical thinking framework has been developed to address the challenges associated with teaching and assessing critical thinking. While there are many definitions of the skill, which are outlined in the first part of this document, few provide a means to operationalise critical thinking in the classroom. This framework outlines critical thinking processes along prescribed strands and aspects informed by a sound evidentiary basis. The aspects contained within the framework are designed to provide foci for teaching and the basis of assessment. This paper is divided into three parts. Part 1 explores the development of critical thinking as an essential skill in 21st-century learning. Part 2 explores how critical thinking has been defined, its association with other skills and describes the dispositions of a critical thinker. Also discussed is the generality of critical thinking principles and skills and its applicability to any subject. Finally, part 3 describes the strands (core elements) that are then further qualified as aspects (sub-elements) of the ACER critical thinking framework .