This chapter establishes a theoretical model for lenticular deployable composite booms based on equilibrium and energy principles, describing load-displacement relationships during flattening (compression/tension) and coiling, and deriving folding moments and ultimate coiling radii. Assuming ultra-thin-walled curved beams, it maintains neutral surface length during flattening, uses polar coordinate polynomials for coiling curvature, and solves stress levels via classical laminate theory and the maximum stress criterion for ultimate radius. Vacuum bag-fabricated samples tested on an INSTRON machine validate load-displacement curves, with stage I linear segment and full nonlinear tension flattening predicted within 22–23% error, and coiling strain predictions matching experimental trends.