Abstract: A collapsible chair includes a frame having two sidepieces, each having a base portion and a back portion. The base has an upward facing concave edge complementary to a portion of a spherical profile of a seating ball, the base portion further includes a frontal aspect. Each sidepiece has one or more hinges to connect the two sidepieces. The sidepieces, when hinged together, are moveable between a collapsed arrangement and an open arrangement. The chair further includes a cross member having an upward facing concave edge complementary to a portion of the spherical profile of the seating ball. The cross member is configured to mate with the frontal aspects of the two sidepieces so as to stabilize the two sidepieces in the open position. The upward facing concave edges of the sidepieces and the cross member form a triangular cradle that supports the seating ball.