In this chapter, four semi-analytical methods for computing the hydrodynamic interactions in arrays of wave energy converters are presented (the point absorber, plane wave, multiple scattering and direct matrix methods). They all target the same solution, attainable under linear wave theory, but utilize varying degrees of further approximation in the derivation. Many of the methods are based on similar principles and involve explicit mathematical expressions corresponding to intuitive physical quantities. Of the methods detailed here, the direct matrix method is perhaps currently the most popular amongst researchers due to the ‘exact’ solution under linear wave theory and simpler solution method than the multiple scattering technique. However, all of the other methods may yet find further use, given the appropriate context. Although semi-analytical techniques were some of the first methods to be used to analyse wave energy device arrays, with many others being subsequently developed and widely utilized, they still find relevance for researchers and other analysts today. Linear wave theory is still widely used in performance and loading calculations, due to the relative speed of implementations compared to more detailed methods such as CFD and their ability to incorporate wave phase effects compared to spectral wave models, for example. In the context of linear wave theory, semi-analytical techniques constitute a complementary approach to more implicit solution methods (such as boundary element methods) for array interaction calculations as a result of the fact that they may be coded relatively simply, provide insight into the problem, are flexible in the manner in which they may be applied and are generally more efficient.