Functional constipation is a common disorder affecting around one in ten children worldwide and negatively impacts quality of life. In this thesis, novel insights in diagnostics and management of constipation in children are discussed. Part 1 focuses on the diagnosis of functional defecation disorders. Chapter 1 describes normal defecation patterns in healthy children. In chapter 2, the intra-rater reliability of diagnosing a functional gastro-intestinal disorder via questionnaire is investigated.Part 2 focuses on the use of anorectal manometry. Chapter 3 describes a randomized controlled trial which evaluates the effect of hypnosis to reduce distress in children undergoing anorectal manometry. In chapter 4 differences between 3D anorectal manometry and regular high-resolution manometry are investigated. Chapter 5 describes characteristics of children diagnosed with internal anal sphincter achalasia. In chapter 6 the effect of anesthesia on anorectal manometry outcomes is evaluated. In chapter 7 anorectal and colonic manometry outcomes are compared between children with and without fecal incontinence. Part 3 includes studies on the management of constipation. Chapter 8 systematically reviews the non-pharmacologic treatment of functional constipation. In chapter 9 the efficacy and side-effects of linaclotide are investigated in children with functional constipation or irritable bowel syndrome with constipation. In chapter 10 the effect of anal botulinum toxin injection is prospectively investigated in children with organic and functional constipation. Chapter 11 investigated the efficacy and patient satisfaction of transanal irrigation in children. In chapter 12, outcomes of antegrade continence enemas in children with functional or organic constipation are prospectively assessed.