Abstract. We develop exact expressions for the coef cients of series representations of translations and rotations of local and multipole fundamental solutions of the Helmholtz equation in spherical coordinates. These expressions are based on the derivation of recurrence relations, some of which, to our knowledge are presented here for the rst time. The symmetry and other properties of the coef cients are also examined, and based on these, ef cient procedures for calculating them are presented. Our expressions are direct, and do not use the Clebsch-Gordan coef cients or the Wigner 3-symbols, though we compare our results with methods that use these, to prove their accuracy. For evaluating a term truncation of the translated series (involving multipoles), compared to previous exact expressions that require operations, our expressions require evaluations.Key words. Helmholtz equation, multipole solutions, translation and rotation coef cients, fast evaluation.AMS subject classi cations. 33C55, 33C10, 35J05, 65N38, 65N99, 65Y201. Introduction. In several scienti c computing applications, the solution to the Helmholtz or Maxwell Equations is expressed in terms of the singular (multipole) and regular solutions of the Helmholtz equation in spherical coordinates, centered at various points. Series of such solutions (see Eq. (2.16)) in one coordinate system must be expressed, in terms of series of singular or regular solutions in another coordinate system. Such expressions are guaranteed to exist by the completeness of the functions on a sphere. Addition theorems [5], [15] provide the expressions for the coef cients of the series in the shifted coordinates, in terms of the original coef cients. The paper by Epton and Dembart [8] provides an introduction to expressions of the coef cients. Chew [22] applied differentiation theorems for spherical functions similar to those in this paper, to obtain recursions for the translation coef cients.One important scienti c computing area where there is a need for such expressions is in the Fast Multipole Method (FMM) solution of the Helmholtz and Maxwell equations [9,27,10]. The FMM algorithm was referred in [1] as one of the top algorithms of the 20th century. Here the complexity of the translation expressions on the one hand, and the numerical accuracy achievable on the other, are key barriers to use of these methods to more complicated problems that are of interest, and these are thus an area of active research. Other scienti c computing areas where there is a need for such translation theorems are in the solution of boundary value problems of scatterings from many spheres [24], and in the use of the T-matrix method for solution of scattering problems from many scatterers [14]. Note that in some multipole methods (e.g. [24]) computation of each entry of the translation matrix is needed. In this case the recursive computation of the matrix elements provides the algorithm with theoretical minimum of asymptotic complexity. For speci c applications we refer the reader to these papers....