The paper deals with the geometric design of deployable scissor structures. These structures are classified as foldable or deployable. A foldable structure guarantees a stress free condition during deployment.A new equation, the foldability equation is derived. The foldability equation is formulated using a purely geometric approach. The foldability vector used in the foldability equation is formulated for some basic units in deployable structures. The foldability equation is then used to analyse the kinematics and determine the foldability/deployability of translational, cylindrical, and spherical configurations.