This paper presents an overview of common-centroid (CC) layout styles, used in analog designs to overcome the impact of systematic variations. CC layouts must be carefully engineered to minimize the impact of mismatch. Algorithms for CC layout must be aware of routing parasitics, layout-dependent effects (for active devices), and the performance impact of layout choices. The optimal CC layout further depends on factors such as the choice of the unit device and the relative impact of uncorrelated and systematic variations. The paper also examines scenarios where non-CC layouts may be preferable to CC layouts.