This book presents papers from the bi-annual meeting of the International Research Society of Spinal Deformities (IRSSD), held as a virtual event on 22 and 23 January 2021. The IRSSD concentrates on research into spinal deformity with clinical applications. In addition to 3D assessment of the spine, researchers also explore spinal biomechanics, etiopathogenesis, and innovative conservative and surgical therapies with the goal of integrating science with clinical care to improve patient care. The 2021 meeting was originally scheduled to take place in Milwaukee, Wisconsin, USA, but was instead held in a virtual format due to the Covid 19 pandemic. Despite this change, the meeting still allowed valuable interaction and open discussion among practitioners from around the world, and keynote speakers and authors contributed the 44 short papers and 47 abstracts included here. The papers are grouped under 17 chapter headings, and cover a wide range of topics, including biologic and biomechanical benchmarks, clinical evaluation, conservative treatments and surgical approaches. Diagnostic assessments and non-surgical treatments of EOS are also emphasized and elucidated.