Proteinuria is an important biomarker commonly used to detect and manage kidney disease in children. There are now a variety of methods available to measure urinary protein loss, and physicians are faced with several contrasting strategies: 24-h or timed collection versus spot samples (first-morning or random), measurement of total urinary protein versus selective measurement of urinary albumin, unadjusted urine protein concentration versus protein-to-creatinine ratio and the use of dipstick versus laboratory-based methods. In this review, we will discuss the advantages and disadvantages of these different approaches. We will then summarise the evidence base for proteinuria as a clinical biomarker in different settings, including discussion of the current and potential role of measuring low-level albuminuria. Finally, we will highlight gaps in the literature and opportunities for further research into proteinuria among children.