The critical load of a system undergoing bifurcation, such as domes and shells, is highly sensitive to imperfections. It is important to capture the “worst imperfection” that reduces the critical load of this system most rapidly. This chapter presents a procedure to determine the worst pattern of imperfections. This procedure is applied to a truss dome structure. Chapter 3, “Imperfection Sensitivity Laws,” is a foundation of this chapter, and this chapter is extended to a system with group symmetry in Chap. 10.