In this chapter, various problem formulations and methods of topology optimization are presented for pin-jointed trusses. A brief introduction and historical review are given in Sec. 3.1. The traditional concept of the Michell truss is presented in Sec. 3.2. Some typical problem formulations and methodologies are summarized in Secs. 3.3 and 3.4. The problem under stress constraints is discussed for continuous variables in Sec. 3.5 and discrete variables in Sec. 3.6. A genetic algorithm is applied in Sec. 3.7 for the problem considering nodal costs. A random search method is presented in Sec. 3.8. An approach based on semidenite programming for eigenvalue constraints is presented in Sec. 3.9. Finally, application of data mining is discussed in Sec. 3.10.