While trying to create a professional development session, author Wanko and one of his undergraduate students were searching, without much luck, for a Sudoku variation that uses some aspect of geometric thinking. However, they noticed that the placement of numbers in a Sudoku solution indicates some basic geometric shapes. For example, four of the 5s in the 6×6 Sudoku solution (see fig. 1b) outline the vertices of a square, and four of the 6s outline the vertices of a parallelogram (see fig. 3). They realized that a Sudoku variation could be created that draws on the solver's knowledge of attributes of geometric shapes. Thus, Shapedoku was born!