Curve stitching is a craft in which a series of geometric forms are used to create the appearance of a curve. While curved stitched designs appear to have complex, graceful curves and a three dimensional aspect, they are actually totally flat, and comprised entirely of straight lines. Also known as string art, curve stitching is not just a craft: it's also an educational tool. Children are sometimes introduced to basic concepts in geometry with the assistance of curve stitching.

English mathematician Mary Everest Boole is generally given the credit for inventing curve stitching. She developed the technique in the early 1900s as an aid for teachers who wanted an interactive method for introducing children to geometry. Curve stitching continues to be used for this purpose, in addition to being popular with some crafters. While other educators and mathematicians have played with the basic idea, few have been able to improve on Boole's basic concepts.

Classically, curve stitching is done on pasteboard, cardboard, or heavy cardstock. A geometric shape is drawn on the stitching surface, and then a needle and thread are used to create a series of straight lines running back and forth from one side of the shape to the other. Each side of the shape is pierced several times with the thread, creating a series of connections between it and a neighboring side. As the lines intersect, the suggestion of a curve is created at the intersections of the line, with the curve appearing more realistic the more lines there are.

The simplest curve stitching project is simply a triangle, which is used to create a simple parabola. People can play with a variety of different designs to create other shapes, including very complex patterns which can look stunning when they are executed in multiple thread colors. The grid of lines can also be created on fabric, rather than paper, or executed with paint, pencils, or a computer program.

A number of curve stitching books are available with pattern suggestions and grids which can be used for curve stitching. As people grow more competent, they can also develop their own designs and play with patterns and variations. Educationally, curve stitching can be quite valuable, as it may get younger students interested in math as they marvel at the patterns they produce and the fact that a series of entirely straight lines can create a shape which appears curved.