Abstract A focus on the excitations of a given nucleus is known as the ‘vertical’ approach to nuclear structure and has been the empirical cornerstone of nuclear physics and the inspiration for countless nuclear models. On the other hand, the ‘horizontal’ approach looks at changes in various observables across different regions of the nuclear chart (or even across the whole chart). This chapter outlines some of the elements of a horizontal approach that focuses on the evolution of the nuclear structure. This approach offers important insights not only about nuclear structure, but also phase transitions in finite nuclei, the properties of newly discovered nuclei, and the underlying shell structure. Two types of approaches, known as valence correlation schemes and correlations of collective observables, are considered. Many of these ideas are especially applicable to the new exotic nuclei that are becoming available with the advent of radioactive beams.