The role of optimization in various practical applications has been increasing over the years. In the field of aerodynamics, design optimization is rapidly evolving in many ways. One of the latest developments in this field is the introduction of surrogates or metamodels. The use of surrogates has a number of advantages especially concerning the computation cost, memory and time budgets. The present paper aims to introduce the topic of surrogate-based optimization. An overview on the main aspects of surrogates and the associated terminology are discussed in detail. In addition, the paper provides a survey over the previous efforts contributing in this field. The paper is finalized with some general recommendations.