The Compendium of Physical Activities (Compendium) was developed to standardize the assignment of physical activity (PA) intensity values in PA epidemiology research. It was first created in 1989, modeled after the Standard Occupational Classification document. The Compendium was developed by Dr. William Haskell and Dr. Barbara Ainsworth, who assigned metabolic equivalent (MET) intensity codes to activities. The Compendium was updated in 2000 and 2011, adding new activities and refining MET values. The 2011 update included new Specific Activity codes and more precise MET values based on systematic literature searches. A website was developed to facilitate access to the Compendium documents. The 2024 update re-named the Compendium as the Adult Compendium of Physical Activities to differentiate it from other compendiums for youth and older adults. The 2024 Adult Compendium includes new activities, updated MET values, and a new website. The Compendium has been widely used by government agencies, schools, and commercial products to standardize PA intensity assignments. It has accumulated over 22,000 citations according to Google Scholar. The Compendium has been updated by Barbara Ainsworth and her network of mentees over the past 35 years. The 2024 Compendium represents a new generation of researchers, led by Dr. Stephen D. Herrmann. The authors contributed to the manuscript, with BEA conceiving and drafting it, and others editing it. The authors declare no competing interests.The Compendium of Physical Activities (Compendium) was developed to standardize the assignment of physical activity (PA) intensity values in PA epidemiology research. It was first created in 1989, modeled after the Standard Occupational Classification document. The Compendium was developed by Dr. William Haskell and Dr. Barbara Ainsworth, who assigned metabolic equivalent (MET) intensity codes to activities. The Compendium was updated in 2000 and 2011, adding new activities and refining MET values. The 2011 update included new Specific Activity codes and more precise MET values based on systematic literature searches. A website was developed to facilitate access to the Compendium documents. The 2024 update re-named the Compendium as the Adult Compendium of Physical Activities to differentiate it from other compendiums for youth and older adults. The 2024 Adult Compendium includes new activities, updated MET values, and a new website. The Compendium has been widely used by government agencies, schools, and commercial products to standardize PA intensity assignments. It has accumulated over 22,000 citations according to Google Scholar. The Compendium has been updated by Barbara Ainsworth and her network of mentees over the past 35 years. The 2024 Compendium represents a new generation of researchers, led by Dr. Stephen D. Herrmann. The authors contributed to the manuscript, with BEA conceiving and drafting it, and others editing it. The authors declare no competing interests.