A mildly interesting notion for a counting book: when Mary's mother waves for a taxi, two bicyclists wave back, then three boys wave at the cyclists, and so on. This rather limited idea is distinguished by Sis's carefully designed illustrations. Sequentially numbered doors on a city street are rendered in grisaille to form a background for details that make playful use of the numbers: e.g., each of six policemen has a horse, and there are a ""Seven Dwarfs Restaurant"" and a lady with ten suitcases watching the ten joggers. The numbers are also hidden in the pictures in Roman numerals, spelled out, and (in one case) in French. After 15 taxi drivers wave back at everyone, Mary and her mother walk home. Although not exceptional, Waving serves its purpose.