Hybrid optimization methods have known significant interest in recent years and are being growingly used to solve complex problems in science and engineering. For instance, the famous evolutionary Genetic Algorithm can integrate other techniques within its framework to produce a hybrid global algorithm that takes advantages of that combination and overcomes the disadvantages. Several forms of integration between Genetic Algorithms and other search and optimization techniques exist. This chapter aims to review that and present the design of a hybrid Genetic Algorithm incorporating another local optimization technique while recalling the main local search methods and emphasizing the different approaches for employing their information. A test case from the aerospace field is presented where a hybrid genetic algorithm is proposed for the mechanical sizing of a composite structure located in the upper part of a launcher.