## 1 Introduction  
Light scattering and absorption by a single sphere, i.e., electromagnetic radiation, is a widely studied canonical problem encountered in both applied and theoretical sciences, such as material and optical physics [1; 2; 3; 4; 5], chemistry [6; 7], nanotechnology [5; 8], radio/antenna engineering [9; 10], and applied mathematics [11]. The sphere is one of the few three-dimensional bounded geometrical shapes that possess a closed-form analytical solution either in the electrostatic or the electrodynamic domain (Here we assume a small-to-intermediate sized sphere with respect to the incident wavelength. Treatments of larger spheres in the geometrical optics approximations are beyond the scope of this short review, see for example [12]). Thus, a sphere can be arguably perceived as an archetype of a scatterer for the extraction of valuable insights regarding the scattering problem by bounded objects. It is commonly used as a reference for any kind of electromagnetic scattering theory [13] and applications, from the utilization on experimental setups [7] to the benchmarking of computational methods [14; 15] and beyond. The twentieth century witnessed the birth of many, now-classical, text-books dealing with light scattering spheres, offering thorough, instructive, and wide discussions on the subject and its treatments. Workers such as [PERSON] [16], [PERSON] [17], [PERSON] [18], and [PERSON] [19] are only some of the contributors to this tradition, delivering complete and educative perspectives on this subject. Indeed, the number of books and contributors on this subject is very large. It is appropriate to acknowledge that this is just an indicative and not comprehensive textbook list. For a more complete list, one can follow the suggested textbooks and the references therein. An eloquent historical retrospective for the research up to the 1970s is given by [PERSON] in his book on light scattering [18]. Nonetheless, the significance of such a long-standing problem with solidly established theory resonates up to our modern times, opening new avenues for the understanding of fundamental scattering and absorptive phenomena. A stark example is the recent identification of Fano interference line-shapes appearing on the scattering spectrum of a sphere [20; 21; 22; 23]. Recent research trends, such as the metamaterial/metasurfaces paradigm [24; 25; 26], and the plasmonic or all-dielectric energy control/harvesting devices [4; 5; 8; 26; 27; 28; 29; 30; 31; 32; 33] enabled the extensive use of a sphere as a fundamental testbed purposes. Likewise, the conceptual demonstration/realization of single particle devices, such as sensors [34; 35], electromagnetic cloaks [36; 37; 38; 39; 40], \"super\"-scatterers [41], optical force carriers [42], and optical memory devices [43], are nothing but different perspectives on the scattering response of a spherical inclusion, and new light control/harvesting functionalities are attributed to the emerging collective effect of a suspension of spherical scatterers [2; 8; 25; 44]. It is therefore evident that the spherical scattering particles are in the core of modern electromagnetics and optics research. In this review, some of the most basic features of its resonant scattering behavior are exposed, covering the two most prominent features of a resonant sphere: the plasmonic and the dielectric resonances. To start with, let us assume a sphere of radius \(r_{1}\) subject to an incident monochromatic plane wave of wavelength \(\lambda\), as can be seen in Figure 1, where the time-harmonic convention \(e^{-i\omega t}\) is assumed. The sphere consists of a homogeneous and isotropic material of given permittivity (dielectric constant) \(\varepsilon_{1}\) and permeability \(\mu_{1}\), immersed in a host medium with relative parameters \((\varepsilon_{\text{host}},\mu_{\text{host}})\). Note that all material parameters are normalized with respect to the permittivity and permeability of vacuum, \(\varepsilon_{0}\), \(\mu_{0}\).