Introduction: An Orientation to the Book and How to Use It 1Désirée B Maltais and Reidun B Jahnsen2 Principles of Health-Related Physical Fitness Assessment and Training 7Tim Takken, Olaf Verschuren, and Erik H Hulzebos3 Safety Considerations 27Haakon Dalen and Reidun B Jahnsen4 Principles of Measuring Physical Activity 39Carol Maher and Dot Dumuid5 How to Promote a Physically Active Lifestyle Across the Lifespan 57Ine Wigernaes, Berit Gjessing, Anne Ottestad, and Kjersti Syvertsen6 Cerebral Palsy 75Désirée B Maltais, Reidun B Jahnsen, and Maria Terese Engdahl-Høgåsen7 Developmental Coordination Disorder 99Sara King-Dowling, Jeffrey D Graham, and John Cairney8 Spina Bifida and Childhood Acquired Spinal Cord Injury 115Ana-Marie Rojas and Shubhra Mukherjee9 Childhood-Onset Neuromuscular Conditions 145Craig Campbell and Katy de Valle10 Intellectual Disability 163Anne-Stine Dolva, Roald Undlien, Kaja Giltvedt, and Andreas T Sandfossen11 Autism Spectrum Disorder 181Ine Wigernaes and Ellen K Munkhaugen12 Juvenile Idiopathic Arthritis 199Kristine Risum