Toilet training is a process in which children learn to urinate and have bowel movements in the toilet. Using the toilet is a developmental milestone, which means that it is one of the events that a doctor uses to tell whether a child is developing at a normal pace.

A child must be both physically and emotionally ready before toilet training can succeed. Some children may be ready to begin toilet training as early as 18 months of age; most are ready to begin toilet training between the ages of 22 and 30 months. Most children are able to successfully use the toilet around age 3, usually some time between 26 months and 38 months of age. Girls usually become toilet-trained a few months earlier than boys.

Stress in the home can delay a child's readiness to become toilet-trained. Attempting toilet training if the child is not physically and emotionally ready leads to frustration for both the parents and the child.